Washington ( CNN ) -- The U.S. government is stepping up its involvement in the Syrian crisis after allegations of chemical weapons use -- with its top military official making plans to respond quickly , and its top diplomat reaching out to Syria 's foreign minister and others in the wake of the report . On Saturday , a senior State Department official said that Secretary of State John Kerry had talked Thursday -- the day after the attack -- with Syrian Foreign Minister Walid Moallem . The purpose of the call was to make clear that if the Syrian government had nothing to hide , it should have allowed immediate access to the site -- rather than continuing to attack the area to block access and destroy evidence , the official said . Meanwhile , the U.S. military was busy in its own right . If claims that Syria used chemical weapons this week are true , a speedy response will be needed to prevent another such attack , Defense Secretary Chuck Hagel said Friday . A senior Defense Department official has told CNN that military planners have updated Syrian target lists . And it was disclosed that a fourth U.S. ship armed with cruise missiles has arrived in the eastern Mediterranean Sea . A United Nations team is in Syria attempting to investigate a claim by the nation 's rebels that a chemical weapons attack by President Bashar al-Assad 's forces outside Damascus killed more than 1,300 people . Hagel addressed the issue aboard a military plane headed to Malaysia . `` We will determine at some point here very shortly what did happen , '' he said , according to an account posted on the Defense Department 's website . `` If , in fact , this was a deliberate use and attack by the Syrian government on its own people using chemical weapons , there may be another attack coming , '' Hagel said . `` A very quick assessment of what happened and whatever appropriate response should be made . '' Hagel said the American military was providing President Barack Obama `` with options for all contingencies , and that requires positioning our forces [ and ] positioning our assets to be able to carry out whatever options the president might choose . '' He did not provide specifics on what the options were . Obama talked Saturday with British Prime Minister David Cameron about Syria , according to a White House statement . Together expressing `` grave concern '' about the chemical weapons reports , the two leaders will `` consult closely '' on the investigation into the incident as well as `` possible responses by the international community , '' according to the White House . Kerry also has been active , reaching out Saturday to Saudi Foreign Minister Saud al-Faisal , Jordanian Foreign Minister Nasser Judeh , Turkish Foreign Minister Ahmet Davutoglu and Arab League Secretary-General Nabil el-Araby , a senior State Department official said . Earlier , in a CNN exclusive interview with `` New Day , '' Obama defended his decision not to intervene militarily in the Syrian conflict . But he predicted that American focus on the civil war would be necessary for the fighting to come to an end . `` I think it is fair to say that , as difficult as the problem is , this is something that is going to require America 's attention and hopefully the entire international community 's attention , '' Obama told CNN 's Chris Cuomo . The president has said he does not anticipate using ground forces in Syria . Other military options could include airstrikes by fighter jets or cruise missiles . The Navy destroyer USS Ramage has arrived in the region , a defense official said late Friday . It was intended to replace the USS Mahan , but the Mahan will remain temporarily along with the USS Gravelly and USS Barry . All four are equipped with cruise missiles . So far , the president has authorized a limited amount of military hardware for the rebels in addition to logistical and humanitarian assistance . The senior Defense Department official who spoke to CNN said options for direct military action would include targeting al-Assad 's capability to deliver chemical weapons . Target lists could include government buildings and military installations , the official said , but the military must have flexible plans to target forces and equipment which `` continue to move . '' Sen. John McCain , an advocate for a more forceful U.S. response to the Syrian conflict , has suggested that American air power could take out runways and planes used by al-Assad 's forces that he said are `` dominating the battlefields and the towns and the cities . '' McCain also has advocated giving rebels anti-aircraft and anti-missile weapons to establish a `` no fly zone . '' But administration officials have cautioned that some Syrian rebel factions have ties to al Qaeda terrorists . Joint Chiefs Chairman Gen. Martin Dempsey said in a letter to a member of Congress this week that arming rebels requires `` choosing one among many sides . '' `` It is my belief that the side we choose must be ready to promote their interests and ours when the balance shifts in their favor . Today , they are not , '' Dempsey wrote . Chris Lawrence reported from Washington . David Simpson reported and wrote from Atlanta . CNN 's Greg Botelho and Jamie Crawford contributed to this report .
NEW : Secretary of State Kerry talks with Syria 's foreign minister on chemical weapon claim . NEW : He told him Syria should have allowed access to site , rather than still be attacking it . U.S. defense secretary : If al-Assad used chemical weapons once , he may do so again . U.S. military planners update target lists for fighters or cruise missiles .