(CNN) Sen. John McCain said Thursday that he might seek a subpoena to gain the information he wants about the attack in Niger that left four US soldiers dead and two wounded. 
 
 "It may require a subpoena," McCain told reporters on Capitol Hill when asked what steps he would be willing to take to get more information. 
 
 The Defense Department is conducting an initial review of the deadly incident, searching for precise answers as to how 50 ISIS-affiliated fighters were able to ambush a group of soldiers two weeks ago. 
 
 McCain, who is the chairman of the Senate armed services committee, said he might not wait for the department to finish its own investigation before seeking those details. 
 
 "That's not how the system works. We're coequal branches of government," McCain told CNN's Suzanne Malveaux. "We should be informed at all times." 
 
 The longtime senator forcefully argued that the Trump administration has not been forthcoming and needs to do a better job of keeping the committee up to speed. 
 
 "We did not know about Niger until it came out in the paper. We need to have a process of communications, which I've had with other administrations, of exchanging information and knowledge," he told reporters. 
 
 However, he said he had a "good conversation" with national security adviser H.R. McMaster Wednesday night and they're currently in the process of scheduling a briefing on the matter. 
 
 Asked Thursday how he felt about McCain's criticism -- that it was easier to get information under previous administrations -- McMaster said, "It hurt my feelings." 
 
 "I love and respect Sen. McCain," he said. "if Sen. McCain says we need to do a better job communicating with him...we're going to do it." 
 
 McCain also signaled that he might hold up defense nominations over the issue. He said he hadn't heard back from the administration after he and Democratic Sen. Ben Cardin sent a letter last week asking why recently approved sanctions against Russia haven't been implemented yet. 
 
 "Why do you think they go past the deadline on all of these things?" McCain asked reporters. "Because they think they can get away with it. That's why we say no nominations and we get the information we need." 
 
 Asked if he was holding up nominations until he gets answers just on Russia sanctions, McCain said, "On everything." 
 
 The Arizona Republican has not gone into detail about what kind of information he was looking for on Niger, saying only that he was interested in "all the specifics." 
 
 "That's why we're called the Senate armed services committee. It's because we have oversight of our military," he said. "So we deserve to have all the information." 
 
 Sen. Jack Reed, the ranking member of the Senate armed services committee, did not express strong agreement with McCain on the idea of a potential subpoena, though he also wanted more information. 
 
 "I hope not," he said. "We're just doing our job, which is to look carefully at what took place. We have to authorize these operations and support them. We have to know what's going on." 
 
 The comprehensive investigation of the timeline has been ordered by US Africa Command and includes all the military branches and elements of US intelligence agencies that were involved in the mission. Team members who were on the ground are being interviewed about what happened as well as preparations for the mission. 
 
 Sen. Mike Rounds, a Republican on the committee, said he felt it was "appropriate" to let the Defense Department finish its investigation before the committee took its next steps. 
 
 "We'll allow General Mattis to do his investigation," he said. "At that point, whether it be in a classified session or an unclassified hearing, I would suspect that we'll have a report delivered." 
 
 White House spokeswoman Sarah Sanders was asked in the press briefing Wednesday whether President Donald Trump was satisfied with the information he has received about the mission and ambush. 
 
 "I believe they're still looking into the details of that," Sanders replied. "But I don't think that the President can ever be satisfied when there's loss of life from men and women in uniform." ||||| Breaking News Emails Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings. 
 
 / Updated By Robert Windrem and Courtney Kube 
 
 The U.S. military is still searching for answers on what happened in Niger two weeks ago when four U.S. soldiers were killed during an ambush, apparently by a branch of ISIS. 
 
 Now the Pentagon's Africa Command (AFRICOM) has sent a team to the African nation to conduct a "review of the facts," according to two U.S. defense officials. The officials are careful not to call the inquiry an investigation, but admit they simply don't know what happened on Oct. 4. 
 
 "We need to collect some very basic raw facts," one defense official said. 
 
 In addition to the Pentagon, a top Senate Republican wants answers. Armed Services Committee Chairman Sen. John McCain of Arizona told reporters this week that the Trump administration was not being forthcoming about what happened in Niger. 
 
 "I want the information that the Senate Armed Services Committee deserves and needs," he said. 
 
 Some of the facts the AFRICOM team needs to collect, said one defense official, are: Where were U.S. forces when the attack occurred? Did they have adequate personal protective equipment and were they prepared for the attack? Was there adequate intelligence in advance of the mission and adequate response to the attack? 
 
 Chadian troops and Nigerian special forces participate in exercises with the U.S. military and its Western partners in Mao, Chad, in March 2015. Jerome Delay / AP file 
 
 The official said the level of confusion during and after the mission was "tremendous." The fourth soldier's body wasn't found until nearly two days after the ambush. 
 
 Pentagon officials say operations in the region have already "tightened up" and there's been an operational "pause" while AFRICOM assesses the situation. 
 
 U.S. officials say the ambush was likely carried out by an ISIS affiliate called ISIS in the Greater Sahara. ISIS-GS is just one of several ISIS affiliates operating in the region. 
 
 The attack "has not been claimed by a terrorist group, but a group claiming association with ISIS, ISIS in the Greater Sahara, is likely responsible," said a US official. A second U.S. official called the group more ISIS "wannabe" than a direct affiliate of the Syrian-based terror group. However, said the official, it would be wrong to suggest ISIS-GS is unsophisticated. 
 
 Sgt. La David Johnson was killed in an ambush in Niger. U.S. Army Special Operations via AP 
 
 The attack and its aftermath have become a political issue in recent days with President Trump under criticism for not initially calling the families of the four killed, for suggesting that prior presidents had not called the families of the fallen, and then for the alleged content of his call to the widow of one of the four soldiers. 
 
 The four Americans were killed Oct. 4 when a 12-man team of soldiers from the 3rd Special Forces Group was operating with approximately 30 Forces Armees Nigeriennes (FAN) on a train-and-advise mission near Tongo Tongo, Niger, just miles from the Mali border. The patrol was seen as routine and in fact had been carried out 29 times in the six months before the ambush, the Pentagon has reported. 
 
 Militants, both Al Qaeda in the Islamic Maghreb (AQIM) and ISIS, have been using a nearby route to travel back and forth into Mali and back to a base camp in Niger, the official said. The partner forces were working to disrupt the so-called rat line and interdict the militants. 
 
 The 12 U.S. soldiers went to the village to get supplies — food and water. As part of the mission, they visited village elders. Special Forces soldiers often conduct "key leader engagements," making contact with local leaders. 
 
 The team was split up, with eight in the key leader engagement and the other four with the vehicles. 
 
 At the conclusion of the meeting, as the Americans were leaving, they were attacked by 40-50 militants with RPGs and AK-47s. The attackers were "well-equipped and trained," one Pentagon official said. 
 
 The U.S. returned fire but the officials still do not know how many militants may have been wounded or killed in the firefight. There was a platoon of Niger soldiers nearby but U.S. defense officials cannot confirm reports that any of them were wounded or killed. 
 
 Armed French Mirage fighter-bombers arrived on scene within about 30 minutes. The planes didn't drop any bombs or fire on the attackers, but U.S. defense officials believe their presence helped break up the firefight. 
 
 One indication of the level of confusion after the attack is that the U.S. military has provided three different answers for who flew the medevac helicopter – first U.S. military officials said it was French military, then that it was the U.S. military. Now, they're saying it could have been a U.S. contractor. 
 
 A U.S. Army carry team transfers the remains of Army Staff Sgt. Dustin Wright of Lyons, Georgia, at Dover Air Force Base in Delaware on Oct. 5, 2017. Wright was killed in Niger. Aaron J. Jenne / U.S. Air Force via Reuters 
 
 If, as officials believe, ISIS-GS carried out the attack, it would be the group's first against American forces. In the past, they have carried out attacks on French counterterrorism forces. 
 
 ISIS-GS was established in 2015 after the group's current leader, Adnan Abu Walid al-Sahrawi, broke from al-Murabitun (an al Qaeda-associated group) and pledged allegiance to ISIS leader Abu Bakr al-Baghdadi and ISIS. U.S. officials said the group usually uses small arms and mortars to conduct ambushes and complex attacks. 
 
 ISIS-GS has not been formally recognized as an official branch of ISIS but its pledge of allegiance to the terror group was acknowledged by ISIS leadership in Syria in October 2016. 
 
 The U.S. has five outposts in Niger as well as a military presence at the international airport in the capital of Niamey, which is in the far west of the country. The U.S. also has a drone base in Agadez in Central Niger from which the U.S. can monitor militant activity as far north as Libya and as far south as Nigeria. ||||| WASHINGTON (Reuters) - U.S. Defense Secretary Jim Mattis said on Thursday the U.S. military did not have all the accurate information on an ambush in Niger earlier this month that killed four U.S. soldiers. 
 
 U.S. Defense Secretary Jim Mattis listens to a question during a joint news conference in New Delhi, India September 26, 2017. REUTERS/Adnan Abidi 
 
 “The loss of our troops is under investigation,” Mattis said before a meeting with his Israeli counterpart at the Pentagon. “We, in the Department of Defense, like to know what we are talking about before we talk and so we do not have all the accurate information yet.” 
 
 “We will release it as rapidly as we get it,” he added. ||||| "The U.S. military does not leave its troops behind and I would just ask you not question the action of the troops who were caught in the firefight and question whether or not they did everything they could in order to bring everyone out at once," he said.
– The Pentagon has dispatched a team to Niger to figure out exactly what happened in an attack two weeks ago that left four US soldiers dead and two others injured, the New York Daily News reports. Despite the deadly attack happening Oct. 4, officials tell NBC News they still have pretty much no idea about what happened. "We need to collect some very basic raw facts," one defense official says, adding the confusion surrounding the attack was "tremendous." According to CNN, we know the US soldiers were conducting an exercise in Niger when they were ambushed by 50 fighters linked to ISIS. The Defense Department review of the ambush hopes to determine if the soldiers were prepared for the attack, if they had protective equipment, if they adequately responded, and more. One person who doesn't want to wait for the Pentagon to get answers: Sen. John McCain. McCain on Wednesday said he believes the Trump administration has more information on the attack than it's sharing with Congress, and he may resort to a subpoena to get that information without waiting on the investigation. "That's not how the system works. We're coequal branches of government," McCain said Thursday. "We should be informed at all times." Jim Mattis says the military doesn't yet have the facts on the attack, Reuters reports. “We, in the Department of Defense, like to know what we are talking about before we talk and so we do not have all the accurate information yet," the Defense secretary said Thursday. He says the administration will release the information "as rapidly as we get it."