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 BAGHDAD — Wielding the threat of sectarian slaughter, Sunni Islamist militants claimed on Sunday that they had massacred hundreds of captive Shiite members of Iraq’s security forces, posting grisly pictures of a mass execution in Tikrit as evidence and warning of more killing to come. 
 
 
 
 
 
 
 
 
 
 The possible mass killing came as militants cemented control of the city of Tal Afar, west of Mosul, after two days of fierce clashes with Iraqi troops, residents and senior security officials said. The city came under mortar attack, sending many residents fleeing toward Sinjar to the west and Mosul to the east. Residents said the militants freed dozens of prisoners. 
 
 Even as anecdotal reports of extrajudicial killings around the country seemed to bear out the Islamic State in Iraq and Syria’s intent to kill Shiites wherever it could, Iraqi officials and some human rights groups cautioned that the militants’ claim to have killed 1,700 soldiers in Tikrit could not be immediately verified. 
 
 But with their claim, the Sunni militants were reveling in an atrocity that if confirmed would be the worst yet in the conflicts that roil the region, outstripping even the poison gas attack near Damascus last year. 
 
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 In an atmosphere where there were already fears that the militants’ sudden advance near the capital would prompt Shiite reprisal attacks against Sunni Arab civilians, the claims by ISIS were potentially explosive. And that is exactly the group’s stated intent: to stoke a return to all-out sectarian warfare that would bolster its attempts to carve out a Sunni Islamist caliphate that crosses borders through the region. 
 
 The sectarian element of the killings may put more pressure on the Obama administration to aid Iraq militarily. In fact, the militants seemed to be counting on it. A pronouncement on Sunday by the group’s leader, Abu Bakr al-Baghdadi, had a clear message for the United States: “Soon we will face you, and we are waiting for this day.” 
 
 The group’s announcement was made in a series of gruesome photographs uploaded to an ISIS Twitter feed and on websites late on Saturday night. Some showed insurgents, many wearing black masks, lining up at the edges of what looked like shallow mass graves and apparently firing their weapons into young men who had their hands bound behind their backs and were packed closely together in large groups. 
 
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 The photographs showed what appeared to be seven massacre sites, although several of them may have been different views of the same sites. In any one of the pictures, no more than about 60 victims could be seen and sometimes as few as 20 at each of the sites, although it was not clear if the photographs showed the entire graves. 
 
 The militants’ captions seemed tailor-made to ignite anger and fear among Shiites. “The filthy Shiites are killed in the hundreds,” one read. “The liquidation of the Shiites who ran away from their military bases,” read another, and, “This is the destiny of Maliki’s Shiites,” referring to Prime Minister Nuri Kamal al-Maliki. 
 
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 Many of the captions mocked the victims. In one photograph, showing a group of young men walking toward an apparent execution site, where armed masked men awaited, the caption read, “Look at them walking to death on their own feet.” 
 
 So far, Iraq’s majority Shiites were not rising to the bait. Grand Ayatollah Ali al-Sistani, their supreme religious leader, issued a statement on Saturday calling for all groups to “exert the highest possible level of self-restraint during this tumultuous period.” And there was little immediate public reaction to the ISIS claims in Baghdad or other southern Iraqi cities. 
 
 A senior Iraqi government official, speaking on the condition of anonymity because he was not authorized to make press statements, said news of the executions was slow to circulate because Twitter and other social media sites had been blocked for days. “I don’t doubt they are real, but 1,700 is a big number,” he said. “We are trying to control the reaction.” 
 
 Acutely aware of the potential for retaliatory violence, some government officials who had heard about the ISIS claims took pains to play them down, confirming only that some executions had taken place in Tikrit, but not on a large scale. 
 
 One Iraqi security official claimed that no more than 11 bodies of executed soldiers were recovered from the Tigris River downstream from the execution site, a group of six and a group of five, although he confirmed that 800 soldiers had been taken prisoner in the area. He also reported finding 17 bodies washed up against a dam near Samarra, another city the militants are fighting for. But he said, “There is no such superstitious number as 1,700 people executed.” 
 
 An official statement posted on the Ministry of Defense’s website denied the executions had taken place at all. 
 
 Still, other officials and human rights representatives, while cautioning that they could not confirm the full 1,700 number being claimed, said that ISIS had shown no compunctions against hunting Shiites. And they reiterated that such horrific claims would go to further the group’s intent to sow chaos. 
 
 “We’re trying to verify the pics, and I am not convinced they are authentic,” said Erin Evers, the Human Rights Watch researcher in Iraq. “As far as ISIS claiming it has killed 1,700 people and publishing horrific photos to support that claim, it is unfortunately in keeping with their pattern of commission of atrocities, and obviously intended to further fuel sectarian war.” 
 
 Col. Suhail al-Samaraie, head of the Awakening Council in Samarra, a pro-government Sunni grouping, confirmed that officials in Salahuddin Province were aware that large-scale executions had taken place, but did not know how many. “They are targeting anyone working with the government side, any place, anywhere,” he said. He said the insurgents were targeting both Sunnis and Shiites, anyone with a government affiliation, but claiming for propaganda reasons that the victims were all Shiites. 
 
 A New York Times employee in Tikrit said local residents saw hundreds of Iraqi military personnel captured when they tried to flee Camp Speicher, a former American military base and airfield now used as an air force training center on the edge of Tikrit. It is still in government hands. 
 
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 Most of those captured were air force cadets, the employee said. Those who were Sunnis were given civilian clothes and sent home; the Shiites were marched and trucked off to the grounds of Saddam Hussein’s old palace in Tikrit, where they reportedly were executed. He added that the bodies had been dumped in the Tigris River, which runs by the palace compound. 
 
 The ISIS photographs appeared to have been taken at that location, the employee said. However, he said he had not spoken to any witnesses who claimed to have seen the executions or the victims’ bodies. 
 
 Ryan C. Crocker, a former ambassador to Iraq and a critic of America’s 2011 withdrawal from that nation after the two countries failed to sign a mutual security pact, said the atrocity claims, proven or not, made it more urgent than ever for Washington to become involved. 
 
 “What this administration has to do is get John Kerry on a plane right now, like we did when I was there, and sit down with Shia, Sunni and Kurdish leaders and help them get to a position of declared national unity. Iraqis have to stand together now,” Mr. Crocker said. Regarding the massacres, he said, “Whatever it is, however many people, it’s clearly an effort to ignite an Iraqi civil war.” 
 
 Political analysts here mostly agreed about the militants’ intent. “The problem now is that you are dealing with emotions and ISIS is trying to provoke the other side to take revenge,” said Ameer Jabbar al-Sa’aedi, a Baghdad-based analyst. “There are extremists among the Shia, too, and if they respond, they could begin killing and not exclude anyone. It would be just like what happened in 2006.” 
 
 Even though Ayatollah Sistani’s statement over the weekend was intended to call for restraint on the part of Shiites, it came after his call just a day before for every Iraqi to take up arms to support the government. 
 
 That appeal was expected to greatly accelerate the formation of volunteer groups to supplement Shiite militias — nominally to fight alongside the Iraqi Army. But during the worst of the sectarian bloodletting in Iraq, from 2005 through 2007, some such Shiite groups were deeply involved in violence that was killing as many as 1,000 civilians each week. 
 
 One militia leader, Abu Bakr al-Zubaidi, from a group called Asaib Al Haq, a hard-line offshoot of the Mahdi Army militia, said he was not surprised to hear of the executions. 
 
 “ISIS regards Shia as their eternal enemy, and they will kill whoever falls in their hands who is Shia, whether they are soldiers, grocers or even singers,” he said. “Our response to that is there will not be any living ISIS prisoner.” ||||| The aircraft carrier USS George H.W. Bush and two other U.S. Navy ships arrived in the Persian Gulf Sunday, as Iraqi troops mobilized to protect their country from a wave of Sunni insurgents taking over cities, and threatening the nation's capital. 
 
 The USS George H.W. Bush — accompanied by the guided-missile cruiser USS Philippine Sea and the guided-missile destroyer USS Truxtun — was ordered to the Persian Gulf Saturday to protect American lives and interests in the region. 
 
 Meanwhile the Islamic State of Iraq and al-Sham (ISIS) launched a raid on Tal Afar, a town near the Syrian border, according to security forces and a local official. The Sunni insurgents have already seized several towns and were advancing toward Baghdad. 
 
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 President Barack Obama said Friday he would not send troops back to Iraq, but he was consulting with his national security team to "prepare a range of other options." 
 
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 Obama urged the Iraqi government to deploy its own troops to defend their nation, and Secretary of State John Kerry said Saturday that U.S. assistance would only be effective if Iraqi leaders put aside their differences to combat the surge of attacks. 
 
 A call by the country's most influential Shiite cleric, Grand Ayatollah Ali al-Sistani, for Iraqis to defend their country sparked an uprising of Shiite men to pick up their arms and push back the Sunni militants, which seemed to slow their progression toward Baghdad. 
 
 Assault on #baghdad stalled as govt and #shiite militias take up arms. #iraq — Richard Engel (@RichardEngel) June 15, 2014 
 
 The turmoil is far from over though, as a suicide attacker detonated explosives in the center of Baghdad Sunday, killing at least nine people and wounding 20, according to police. 
 
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 And a series of pictures distributed on what purported to be an ISIS Twitter account showed gunmen from the terrorist group shooting dozens of unarmed men. The authenticity of those pictures has not been independently verified by NBC News. 
 
 Prime Minister Nuri al-Maliki has vowed to defeat the rebel fighters. 
 
 U.S. Senator Lindsey Graham on Sunday said that the United States needs Iran's involvement to prevent a catastrophe in Iraq. 
 
 "We are probably going to need their help to hold Baghdad," Graham, a South Carolina Republican, said on CBS' "Face the Nation." 
 
 "The Iranians have an interest. They have Shia populations to protect. We need a dialogue of some kind," he said. 
 
 — Elisha Fieldstadt, with Reuters ||||| Story highlights The Iraqi air force killed more than 200 ISIS militants, according to Iraq state TV 
 
 U.S. may try to speak directly to Iran about deteriorating Iraq situation, senior U.S. officials say 
 
 Dozens of U.S. military personnel arrive at U.S. Embassy, a U.S. official says 
 
 Photos appearing online appear to show ISIS fighters executing Iraqi security forces 
 
 The Iraqi air force struck back at the militant group ISIS , the Islamic State in Iraq and Syria, killing more than 200 militants, Iraqi state TV reported Monday morning. The air raids took place in Saqlawiyah, northwest of Fallujah, according to a graphic run by state TV. 
 
 ISIS has been ruthlessly fighting to take control of Iraq and has apparently posted chilling photos on jihadi Internet forums seeming to show the executions of Iraqi security forces. 
 
 CNN cannot independently confirm the authenticity of the images purportedly posted by ISIS . CNN is examining the terrain in the images, some of the signage on buildings in several of the pictures and the uniforms of the apparent victims. Those details suggest the photos are real and were taken in Iraq. 
 
 A caption on some of the images reads: "apostates heading to their hole of doom." 
 
 ISIS, an al Qaeda splinter group, wants to establish a caliphate, or Islamic state, that would stretch from Iraq into northern Syria. The group has had substantial success in Syria battling Syrian President Bashar al-Assad's security forces. 
 
 On Friday, a tweet on what was claimed to be an ISIS Twitter account claimed that its members killed at least 1,700 Shiites. CNN was unable to verify the authenticity of the account, and the account appeared to have been taken down Sunday. 
 
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 In a statement, the U.S. State Department condemned the claim by ISIS, also known as ISIL, the Islamic State of Iraq and the Levant. 
 
 "The claim by the Islamic State of Iraq and the Levant (ISIL) that it has massacred 1700 Iraqi Shia air force recruits in Tikrit is horrifying and a true depiction of the bloodlust that these terrorists represent. While we cannot confirm these reports, one of the primary goals of ISIL is to set fear into the hearts of all Iraqis and drive sectarian division among its people," part of the statement read. "Terrorists who can commit such heinous acts are a shared enemy of the United States, Iraq, and the international community. " 
 
 The militants' quick advance in Iraq has been helped by many Sunnis who feel that the Shiite-dominated government has marginalized them. 
 
 ISIS seized Iraq's second-largest city, Mosul, last week and has threatened to march on Baghdad, Iraq's capital and largest city. 
 
 But "Mosul didn't fall," a defiant Iraqi Prime Minister Nuri al-Maliki told military leaders in Baghdad in a speech televised Sunday on state TV. "The ones who have fallen are the politicians who have bet against Iraq." The Prime Minister said, "We will not allow anyone to divide the Iraqi people." 
 
 Al-Maliki called on his top brass and soldiers to march and fight against ISIS, while criticizing Iraqi politicians conspiring against their homeland and Iraqi soldiers who have refused to continue to fight when confronted by ISIS. 
 
 "We will march on every inch, with all our weapons, with all our will and faith, so we can liberate and cleanse every inch of Iraq -- from the southernmost point to the furthest point in the north," he exhorted the military leaders. 
 
 Despite al-Maliki's bold statements, ISIS accumulated several victories across Iraq on Sunday. 
 
 The northwest Iraqi city of Tal Afar fell to ISIS, according to Iraqi Gen. Mohammed al-Quraishi. Many Tal Afar residents -- ethnic minority Shiite Turkmen -- fled the fighting north toward Iraq's Kurdish region. Tal Afar is in Nineveh province, midway between the country's border with Syria and Mosul, north of Baghdad. 
 
 Before Iraqi security forces lost Tal Afar, several mortar rounds landed on a busy area in the town and killed at least seven and wounded 33 people, security officials in Baghdad and Tal Afar told CNN. 
 
 Also Sunday, ISIS gained control of two villages in Adhaim, in its first push into Diyala province, northeast of Baghdad. 
 
 On top of that, Iraqi security forces and gunmen believed to be ISIS clashed near al-Khalis, about 18 miles from Diyala's capital, Baquba, al-Khalis police officials told CNN. Three mortar rounds landed near a recruitment center opened recently for volunteers to help the Iraqi army fight against ISIS. 
 
 Baquba is about 37 miles northeast of Baghdad. Baquba is an ethnically-mixed city, though Sunnis represent a slight majority. 
 
 Given Baquba's proximity to Baghdad, if Baquba were to fall, it could give ISIS militants three-pronged access to Baghdad -- from Anbar province to the west, Ninevah and Salahuddin provinces to the north and from Diyala province from the northeast. 
 
 Meanwhile, on Sunday, CNN Senior International Correspondent Arwa Damon was in the Iraqi Kurdish province of Kirkuk, where last Thursday militants took control of two villages. 
 
 She asked the local governor, Dr. Najmaldin Karim, whether the United States should launch airstrikes to help fight back ISIS. 
 
 "I think they know how to do it, but blanket bombing is not going to work here," Karim said, explaining that that approach ignores the fact that ISIS is too blended into the civilian population in Kirkuk and innocent people could die. But there should be targeted bombing in both Iraq and Syria, he said. 
 
 "I don't think anyone is safe from these people," said Karim. 
 
 Partial staff relocation at U.S. Embassy 
 
 Between 50 and 100 U.S. Marines and U.S. Army personnel have arrived at the U.S. Embassy in Baghdad, a U.S. official told CNN on Sunday. 
 
 A U.S official acknowledged to CNN that the additional embassy security personnel being added include U.S. Marines who specialize in embassy protection during high-threat conditions. 
 
 The U.S. invaded Iraq in 2003. American military forces ended their withdrawal from the country in December 2011. 
 
 At the time of the U.S. drawdown, Iraq's leadership had agreed that a residual U.S. military presence was desirable, but the talks broke down over the prickly issue of legal immunity for U.S. troops in Iraq. 
 
 The Obama administration had said any deal to keep U.S. troops in Iraq beyond the withdrawal deadline would require a guarantee of legal protection for American soldiers. But the Iraqis refused to agree to that, opening up the prospect of American troops being tried in Iraqi courts and subjected to Iraqi punishment. 
 
 This week, President Barack Obama continued to consider options with regard to the situation in Iraq but ruled out sending troops into the country. 
 
 On Sunday, U.S. State Department spokeswoman Jen Psaki said that some U.S. security personnel will be added to the staff at the U.S. Embassy in Baghdad and other staff members will be temporarily relocated to consular offices in Basra and Irbil and to the Iraq Support Unit in Amman, Jordan. 
 
 A "substantial majority of the U.S. Embassy presence in Iraq will remain in place," Psaki said in a statement, and "the Embassy will be fully equipped to carry out its national security mission." 
 
 Pentagon Press Secretary Rear Adm. John Kirby said that a "small number of Defense Department personnel" are augmenting State Department security assets in Baghdad. Kirby said that the relocation of some embassy personnel is being done with commercial, charter and State Department aircraft flights. 
 
 The U.S. military can airlift people if the State Department asks for that, Kirby said. 
 
 The State Department is warning U.S. citizens against "all but essential travel to Iraq." The official travel warning says U.S. citizens in Iraq "remain at high risk for kidnapping and terrorist violence." 
 
 While that continues, Iran has recently entered the fray, according to a senior security official in Baghdad who spoke to CNN on Friday. That official said that in recent days, Iran has sent about 500 Iranian Revolutionary Guard troops to fight alongside Iraqi government security forces in Iraq's Diyala province. 
 
 However, Iranian officials, including President Hassan Rouhani , denied reports that some of its elite forces are in Iraq to help bolster al-Maliki, a fellow Shiite. 
 
 "If the Iraqi government wants us to help, we will consider it," Rouhani said, according to an English translation of his remarks Saturday in Farsi by state-run Press TV. 
 
 But, he said, "so far they have not asked specifically for help," and added that Iran could give strategic guidance if requested. 
 
 The Obama administration is exploring possible direct talks with Iran over the deteriorating situation in Iraq, two senior U.S. officials tell CNN. 
 
 Both officials ruled out any type of teaming up with Iran because the United States and Iran don't have a lot of common interests -- other than a stable Iraq. 
 
 The United States is wary of furthering Iran's already considerable influence in Iraq. The Shiite Iranian regime is al-Malaki's closest ally in the region. Additionally the administration is concerned appearing to team up with Iran would both alienate Iraq's Sunni majority and worry Sunni allies of the United States in the region. 
 
 The State Department statement said the United States "will do its part to help Iraq move beyond this crisis," and a senior State Department officer told CNN that Kerry spoke to his counterparts from Jordan, the UAE, Saudi Arabia and Qatar to discuss the threat posed by ISIS. 
 
 The administration has not yet determined what the mechanism would be for talking to Iran, the senior U.S. officials said. 
 
 Ex-U.S. ambassador: Kerry should go to Iraq 
 
 On Sunday U.S. Sen. Lindsey Graham argued on CNN's "State of the Union" for more intervention in Iraq. 
 
 The South Carolina Republican, a frequent critic of the Obama administration's approach to foreign policy, called Obama "stubborn-headed," "delusional" and "detached" over his decision on how to react to the unfolding crisis. 
 
 "Time is running out to turn this around," Graham said. "Get involved with air power. Stop the march toward Baghdad. Deal with Syria. But get a new government (in Iraq) in place as quickly as you can that will bring the Iraqis back together for a counteroffensive." 
 
 Ryan Crocker, the U.S. ambassador to Iraq from 2007 to 2009, told CNN's Fareed Zakaria on Sunday that he thinks Secretary of State John Kerry should fly to Iraq immediately. 
 
 "We need the secretary of state out there in Baghdad right now," Crocker said. "We need the President on the phone to the Iraqi leadership because the reality is the Iraqis are not in a position ... they were not in a position when I was there, they are not in a position now, to work out hard compromises on their own." 
 
 The United States is the "middleman among Sunni, Shia and Kurds," Crocker said. "Ambassadors can go just so far." 
 
 Crocker, now the dean of the George Bush School of Government & Public Service at Texas A&M University, said he would support "very carefully targeted airstrikes" in conjuction with high-level diplomacy. 
 
 "We have got to help the Iraqis come together," Crocker urged, "in a unified fashion to confront a common threat." ||||| Whatever the United States or Iran does in response to the Iraqi crisis, there are wider international considerations at stake. Washington Institute Senior Fellow Michael Eisenstadt joins WSJ's Michael Casey on the News Hub to discuss. Photo: AP 
 
 The radical Sunni militia that has plunged Iraq into chaos bragged on Sunday that it had executed hundreds of Shiite Iraqi soldiers, even as the Obama administration said it is preparing to open direct talks with Iran on how the two longtime foes can counter the insurgents. 
 
 The U.S.-Iran dialogue, which is expected to begin this week, will mark the latest in a rapid move toward rapprochement between Washington and Tehran over the past year. It also comes as the U.S. and other world powers try to reach an agreement with Iran by late July to curb its nuclear program. 
 
 Sunni militants have captured the key northern Iraqi town of Tal Afar, adding to the vast area of territory that Iraq's government lost to insurgents last week. WSJ's Robert Ourlian joins Michael Casey on the News Hub with exclusive details. Photo: AP 
 
 The U.S. and Iran have publicly committed in recent days to provide military support if requested to Iraqi Prime Minister Nouri al-Maliki and help his government repel an offensive the Islamic State of Iraq and al-Sham, or ISIS, has launched against Baghdad and other major Iraqi cities over the past week. 
 
 The U.S. over the weekend repositioned military equipment throughout the region and sent an aircraft carrier to the Persian Gulf as President Barack Obama awaited options for possible military action. 
 
 The U.S. also beefed up security at its embassy in Baghdad and shifted some personnel elsewhere in the country. 
 
 Iraqi officials said on Sunday that ISIS had taken control of Tal Afar in northwest Iraq, where thousands of U.S. and Iraqi forces once fought. The U.S. had hailed the city as a model of its "clear, hold and build" strategy in Iraq. 
 
 View Slideshow This image posted on a militant website appears to show militants from the Islamist State of Iraq and al-Sham leading away men in plain clothes. The Sunni militant group has posted photos that appear to show its fighters shooting dead dozens of captured men. Associated Press 
 
 The possible depth of the ISIS threat became clearer on Sunday when photos were posted on a Twitter TWTR +1.89% Twitter Inc. U.S.: NYSE $38.74 +0.72 +1.89% AFTER HOURS $38.73 -0.01 -0.03% P/E Ratio N/A Market Cap $22.43 Billion Dividend Yield N/A Rev. per Employee $295,368 06/18/14 How Estée Lauder Creates Effec... 06/18/14 When Is It OK to Check a Smart... 06/18/14 Animated GIFs Finally Come to ... More quote details and news » TWTR in Your Value Your Change Short position account associated with ISIS claiming to show Sunni militants carrying out a mass execution of captured Iraqi Shiite soldiers, raising the prospect of a broader sectarian war in Iraq. 
 
 The photographs, accompanied by captions boasting that as many as 1,700 soldiers had been executed, underscored the mounting sectarian animosity fueling the fighting between Sunni extremists and Mr. Maliki's Shiite-dominated government. 
 
 The photographs appear to show dozens of men in civilian clothes in captivity. Captions on the photos describe say the men were being taken away to their deaths. 
 
 In one image, men are shown being transported in trucks. Another image shows armed men wearing black ISIS bandanas pointing their guns toward a clutch of men lying face down in ditch. Still another shows the same men with bloody wounds to their heads. 
 
 If the claim of carrying out mass executions in Iraq is true, pressure could increase on Shiites to retaliate, raising the prospect of a wave of reprisal killings reminiscent of the bloodshed that convulsed Iraq in the years following the U.S.-led invasion of Iraq in 2003. 
 
 While the photographs were posted on a Twitter account associated with ISIS, neither the alleged death toll nor the identity of the purported victims could be verified independently. 
 
 As the U.S. and Iran prepare for talks on the declining situation in Iraq, experts say that Washington should not engage with terrorist organizations. The WSJ's Deborah Kan speaks to Jonathan Schanzer, vice president for research at the Foundation for Defense of Democracies. 
 
 But Ahmed Abdullah Al Jibouri, the governor of Salah Al Din province, where the mass atrocity supposedly took place, said that ISIS had captured "hundreds" of Iraqi military personnel and Air Force Academy students and is believed to have executed them. 
 
 Mr. Jibouri said that the exact number of dead was unknown, since government officials have been unable to reach the alleged sites of the massacre. 
 
 In Washington, State Department spokesperson Jen Psaki said the U.S. couldn't confirm reports of the massacres but called the claim by ISIS "horrifying and a true depiction of the blood lust that these terrorists represent." 
 
 U.S. officials said it is imperative for Washington to discuss the security situation in Iraq with Iran and other regional powers in a bid to better coordinate a response against ISIS. 
 
 Secretary of State John Kerry communicated Washington's strategy to his Iraqi counterpart, Hoshyar Zebari, in a phone call on Saturday, according to the State Department. 
 
 Iranian President Hasan Rouhani said on Saturday that his government was open to cooperating with the U.S. in Iraq and that he exchanged letters with President Obama. 
 
 "When the U.S. takes action, then one can think about cooperation," Mr. Rouhani said at a news conference in Tehran. "Until today, no specific request for help has been demanded. But we are ready to help within international law." 
 
 The U.S. officials said it wasn't certain yet which diplomatic channel the Obama administration would use to discuss the Iraq situation. 
 
 The Islamic militant group that seized much of northern Iraq posted photos that appear to show its fighters executing captured Iraqi soldiers. Associated Press 
 
 One avenue could be through Vienna, where senior American and Iranian diplomats will convene starting Monday as part of international negotiations aimed at reaching a comprehensive agreement to curb Tehran's nuclear capabilities. 
 
 Iran's chief negotiator, Foreign Minister Mohammad Zarif, served as a key interlocutor between Iran and the George W. Bush administration after the Sept. 11, 2001, terrorist attacks on New York and Washington, said U.S. officials. 
 
 Both countries at the time sought to remove the Taliban, a Sunni extremist group, from power in Afghanistan and install President Hamid Karzai. 
 
 "Whatever dialogue may or may not be taking place [with Iran] would take place on the sideline or outside the mainstream of the nuclear talks" in Vienna, Mr. Kerry said Saturday in London. "We don't want that linked and mixed." 
 
 American and Iranian officials over the past year have used a series of bilateral channels—many in secret—to discuss the nuclear issue. Last week, senior White House and State Department officials met their Iranian counterparts in Geneva but didn't discuss the Iraq crisis, according to U.S. officials. 
 
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 The U.S. and Iran rarely see each other as allies. However with new uprisings in Iraq threatening the Shiite led government, installed previously by the United States, both see a reason to work together. Photo: Associated Press 
 
 The White House's engagement with Iran on Iraq offers both opportunities and risks, said U.S. defense officials and Arab diplomats. 
 
 Iran, a majority Shiite country, has served as Mr. Maliki's closest Mideast ally and has mobilized Tehran's military and religious establishment to support their coreligionists in Iraq in recent days. Iran's elite military unit, the Islamic Revolutionary Guards Corps, has an extensive presence inside Iraq, said U.S. officials, and has trained Shiite militias that have joined the Iraqi army in fighting ISIS. 
 
 U.S. officials say the IRGC trained many of the largest Shiite militias going back to the Iraq war and maintain contacts. These include the Mahdi Army, Kata'ib Hezbollah, and Asab Ahl al-Haq. 
 
 Iran has publicly denied sending forces to fight in Iraq and has said it would give Iran military assistance if Iraq asked. 
 
 Even some of Mr. Obama's harshest critics in Washington voiced support on Sunday for coordinating the U.S.'s military response in Iraq with Tehran's. They argued that ISIS poses a much greater near-term threat to the U.S.'s national-security interests than does Iran. 
 
 "Why did we deal with Stalin? Because he was not as bad as Hitler," Sen. Lindsey Graham (R., S.C.) said Sunday on CNN. "The Iranians can provide some assets to make sure Baghdad doesn't fall." 
 
 A number of U.S. defense officials, however, said Iran has a drastically different vision for Iraq than does the U.S. The Iranian government has also supported Mr. Maliki's policies of marginalizing Iraq's minority Sunni population politically and economically, which has fueled support for the ISIS's military operations in the Sunni regions of Iraq. 
 
 Any U.S. military campaign in Iraq that is seen as allied with Iran's and the Shiite majority's risks further polarizing the country, said these officials. It could also alienate Washington's allies in Sunni-dominated countries like Saudi Arabia, Turkey and Jordan. 
 
 "This is a case where the enemy of our enemy is still our enemy," said a U.S. defense official who has worked extensively in Iraq. "Any shared interests in Iraq are limited." 
 
 U.S. allies in Israel and the Middle East are also concerned that any cooperation between Washington and Tehran on Iraq could complicate the nuclear negotiations. 
 
 The Obama administration and its diplomatic partners in the United Nations Security Council have set a July 20 deadline to reach an agreement limiting Iran's nuclear capabilities. 
 
 But U.S. and European diplomats have warned that the gaps between Washington's and Tehran's negotiating positions remain wide, raising serious doubts that an agreement can be reached by July. 
 
 Mr. Rouhani took a hard-line position on the nuclear issue during his Saturday news conference. He said Tehran wouldn't significantly reduce its capacity to produce nuclear fuel through the enrichment of uranium—a key Western demand. And he argued that the U.S.'s sanctions against Iran over the nuclear issue are starting to fray. 
 
 "During the nuclear negotiations we have displayed our strong commitment to diplomacy," Mr. Rouhani said. "If a deal can't be reached by July 20, conditions will never be like the past. The sanctions regime has been broken." 
 
 Israeli and Arab officials have voiced concern that the U.S. won't be able to maintain a tough line on the nuclear issue if its cooperating with Tehran in Iraq. Senior administration officials have denied this. 
 
 In Iranian political circles, momentum is building about the prospect of Iran cooperating with the U.S. to contain the threat of al Qaeda reaching Iran's borders, said several Iranian diplomats and politicians. 
 
 "Some of us realize that is the best opportunity for Iran to improve its diplomatic relations with the U.S.," said a prominent politician in Tehran close to the government. 
 
 During the Iraq war, the two sides occasionally discussed security interests, but through intermediaries such as Kurds. 
 
 The current diplomatic climate may be ripe for Iran to openly engage with the U.S. and use it as an opening for normalizing relations. 
 
 A key factor is that the taboo of direct dialogue with the Americans was broken when Messrs. Obama and Rouhani spoke on the phone during the U.N. General Assembly in New York last fall. Senior American and Iranian diplomats have an open communication channel under the umbrella of the continuing nuclear negotiations between Iran and world powers. 
 
 The intelligence data gathered by Iran's elite Quds Force, the overseas branch of the IRGC present in both Syria and Iraq, would be valuable to the U.S. if it chose to take action against ISIS. 
 
 "Iran and the U.S. are the only two countries with the power to end Iraq's crisis in a peaceful way," tweeted Hamid Aboutalebi, a top political adviser of Mr. Rouhani, on Sunday. 
 
 For Iran, the incentive to cooperate with the U.S. on Iraq goes further than just a desire to improve relations with the U.S., many observers say. ISIS is one of the biggest security threats Iran has faced since the U.S. invaded Iraq in 2003, establishing military bases across the Islamic Republic's borders. 
 
 "Iran is definitely willing to cooperate with the U.S. over Iraq because the threat it's facing is one of existential national security," said Saeed Leylaz, a political analyst close to the government, in a phone interview from Tehran. 
 
 —Farnaz Fassihi, Ellen Knickmeyer and Dion Nissenbaum contributed to this article. 
 
 Write to Jay Solomon at jay.solomon@wsj.com, Carol E. Lee at carol.lee@wsj.com and Farnaz Fassihi at farnaz.fassihi@wsj.com 
 
 Corrections & Amplifications 
 
 Nouri al-Maliki is Iraq's prime minister. An earlier version of this article said he is president. ||||| Tribal fighters and members of Iraqi security forces take part in an intensive security deployment on the outskirts of Diyala province June 14, 2014. 
 
 MOSUL/BAGHDAD (Reuters) - The insurgent offensive that has threatened to dismember Iraq spread to the northwest of the country on Sunday, when Sunni militants launched a dawn raid on a town close to the Syrian border, clashing with police and government forces. 
 
 As the rapid advance south by the Islamic State in Iraq and the Levant (ISIL) towards Baghdad appeared to slow over the weekend, fierce fighting erupted in the town of Tal Afar 60 km (40 miles) west of Mosul near the Syrian border, security sources and a local official said. 
 
 ISIL fighters and other Sunni Muslim armed groups have stormed several towns on the road to Baghdad after seizing Mosul nearly a week ago - an offensive which only stalled as it approached the mainly Shi'ite capital. 
 
 The advance alarmed both Prime Minister Nuri al-Maliki's Shi'ite supporters in Iran and officials in the United States, which helped bring him to power after its 2003 invasion that toppled Sunni dictator Saddam Hussein. 
 
 U.S. President Barack Obama said on Friday he was reviewing military options, short of sending troops, to combat the insurgency, and Iran held out the prospect of working with its longtime U.S. arch-enemy to help restore security in Iraq. 
 
 Maliki's security forces and allied militias regained some territory on Saturday, easing part of the pressure on his Shi'ite-led government, and officials said they were regaining the initiative. Maliki has vowed to rout the insurgents. 
 
 But Sunday's fighting in Tal Afar, a majority Turkomen town which is home to both Shi'ites and Sunnis, showed how volatile the deepening sectarian divisions have become. 
 
 Residents in Sunni districts accused Shi'ite police and army forces of launching mortar fire at their neighbourhoods, prompting ISIL forces stationed outside the town to move in. 
 
 "The situation is disastrous in Tal Afar. There is crazy fighting and most families are trapped inside houses, they can’t leave town," a local official said. "If the fighting continues, a mass killing among civilians could result." 
 
 Government forces are using helicopter gunships against ISIL on the outskirts of Tal Afar, a member of Maliki's security committee told Reuters. 
 
 Over Mosul, an Iraqi military jet came under anti-aircraft fire from ISIL fighters, witnesses said. It was not immediately clear whether it was preparing to attack ISIL positions or was carrying out reconnaissance. 
 
 BAGHDAD BOMB 
 
 In Baghdad on Sunday, a suicide attacker detonated explosives in a vest he was wearing, killing at least nine people and wounding 20 in a crowded street in the centre of the capital, police and medical sources said. 
 
 At least six people were killed, including three soldiers and three volunteers, when four mortars landed at a recruiting centre in Khlais, 50 km (30 miles) north of Baghdad. 
 
 Volunteers were gathered by army to join fighting to regain control of the northern town of Udhaim from ISIL militants. 
 
 They were some of the thousands who responded to a call by the country's most influential Shi'ite cleric to take up arms and defend the country against the hardline insurgents, many of whom consider Shi'ites as heretics. 
 
 A series of pictures distributed on a purported ISIL Twitter account appeared to show gunmen from the Islamist group shooting dozens of men, unarmed and lying prone on the ground. 
 
 Captions accompanying the pictures said they showed hundreds of army deserters who were captured as they tried to flee the fighting. They were shown being transported in the back of truck and led to an open field where they laid down in rows and shot by several masked gunmen. In several pictures, the black Islamist ISIL flag can be seen. 
 
 Most of the captured men were wearing civilian clothes, although one picture showed two men in military camouflage trousers, one of them half covered by a pair of ordinary trousers. 
 
 "This is the fate of the Shi'ites which Nuri brought to fight the Sunnis," a caption to one of the pictures reads. Others showed ISIL fighters apparently seizing facilities in Tikrit, Saddam Hussein's hometown. 
 
 It was not immediately possible to verify the authenticity of the pictures. 
 
 Across the border, a Syrian government air raid hit near ISIL's headquarters in the eastern city of Raqqa, activists said. 
 
 Raqqa, the first and only Syrian city to fall to insurgents since Syria's conflict began more than three years ago, has been a major base for ISIL since it evicted rival rebels including al Qaeda's Syrian affiliate during infighting this year. 
 
 The Britain-based Syrian Observatory for Human Rights said warplanes targeted the governorate building, a large structure in the centre of town, as well as two other buildings, including a sharia, or Islamic law, court. 
 
 Images posted by ISIL supporters online showed a hole surrounded by rubble in the pavement outside the governorate building, although the date and authenticity could not be verified. It was unclear if the building itself was damaged. 
 
 There were no immediate reports of casualties. 
 
 While expressing support for Iraq's government, the United States has stressed the need for a political solution to a crisis threatening to fracture the country less than three years after the U.S. military withdrawal. 
 
 Secretary of State John Kerry told Iraq's foreign minister in a call on Saturday that U.S. assistance would only succeed if Iraqi leaders set aside their differences and forged the national unity needed to confront the insurgent threat. 
 
 The United States ordered an aircraft carrier moved into the Gulf on Saturday, readying it in case Washington decides to pursue a military option after insurgents overran areas in the north and advanced on Baghdad. 
 
 Oil prices have risen to the highest level this year over fears of the violence disrupting exports from OPEC member Iraq. 
 
 Arab League Secretary General Nabil Elaraby said Arab foreign ministers will discuss the "dangerous situation in Iraq" at a meeting in the Saudi city of Jeddah in the next two days. 
 
 In Cairo, a meeting of Arab League ambassadors condemned the "terrorist danger" facing Iraq but did not discuss military assistance. 
 
 (Additional reporting by Isabel Coles and David Sheppard in Arbil, Raheem Salman in Baghdad and Alexander Dziadosz in Beirut; Editing by Giles Elgood) ||||| Advertisement Continue reading the main story 
 
 
 
 
 
 
 
 Insurgents set off two bombs in separate incidents in central Baghdad on Sunday, killing as many as 21 people, witnesses said, and breaking a recent although brief lull in attacks in Iraq’s capital city. 
 
 One attack targeted a market near the Green Zone that sells new and used military uniforms. At the time of the bombing the market was crowded with volunteers seeking to join the fight against insurgents who have swept through much of northern Iraq in the past week. Witnesses at the scene, in the Al-Bab Al-Sharqi area close to Tahrir Square, said 15 people were killed and eight wounded in the midday attack by a suicide bomber wearing a vest full of explosives. Officials put the death toll at nine. 
 
 “I picked up the head of the suicide attacker by my own hands,” said Ahmed Al-Fatlawi, 33, who sells clothes and who said two of his friends were killed in the attack. “He was a youth with a big beard.” 
 
 Earlier, about 7 a.m. Sunday, a car bomb exploded at a bus station in southern Baghdad’s Bab al-Sheikh neighborhood, killing 12 people and injuring 30, according to a security official who spoke on the condition of anonymity because he was not authorized to do so publicly. 
 
 The last major suicide attack was on Wednesday, when 21 people were killed in the largely Shiite Sadr City neighborhood. On June 7, a spate of attacks throughout Shiite neighborhoods in Baghdad killed at least 48 people.
– As fighting rages today across Iraq, Washington is beginning to take action. About 50 to 100 Marines and Army personnel are now at the US embassy in Baghdad, and some embassy staff have been moved to other consular offices in Iraq and Jordan, CNN reports. Meanwhile, US Navy ships including the aircraft carrier USS George HW Bush have arrived in the Persian Gulf, NBC News reports. And the Wall Street Journal reports that the US is planning to begin direct talks with Iran this week about ways of curbing Sunni militants in Iraq. In other news: The militants who seized much of western and northern Iraq say they've recently executed 1,700 people, the New York Times reports. No official confirmation yet, but the Islamic State of Iraq and Syria posted gruesome images of massacre sites on Twitter. Most victims are reportedly Shiite Iraqi soldiers, but Sunnis affiliated with the government were among the dead. The Grand Ayatollah Ali al-Sistani revised the call to arms he issued Friday, apparently concerned about a possible wave of Sunni/Shiite reprisal killings. He urged Iraqis "to exert the highest level of self-restraint during this tumultuous period." Militants clashed with security forces near al-Khalis, northeast of Baghdad, and took over the town of Tal Afar, near the Syrian border. Sunni residents in Tal Afar say Shiite forces bombed their neighborhoods with mortar fire, Reuters reports. Two bomb attacks today killed up to 21 people in central Baghdad, one in a market full of volunteers assembled to join the fight against militants, the New York Times reports. See where ISIS militants came from, or how they became "insanely wealthy."