The Pentagon is prepared to carry out military options on Syria should President Barack Obama choose to exercise any of them, US Defense Secretary Chuck Hagel said on Sunday.
"President Obama has asked the Defense Department to prepare options for all contingencies. We have done that and we are prepared to exercise whatever option - if he decides to employ one of those options," Hagel told reporters during a trip to Malaysia.
Obama has been reluctant to intervene in Syria's civil war, but reports of the killings near Damascus have put pressure on the White House to make good on the president's comment a year ago that chemical weapons would be a "red line" for the United States.
The United States is repositioning naval forces in the Mediterranean to give Obama the option for an armed strike.
US military and national security advisers presented Obama on Saturday with a range of options for responding to the alleged use of chemical weapons by the Syrian government, the White House said.
Obama met with top advisers including Vice President Joe Biden, national security adviser Susan Rice, and CIA Director John Brennan to hash out responses.
The White House declined to list what options were discussed on Saturday and said Washington was still gathering details about the attack.
Obama also spoke with British Prime Minister David Cameron, a top US ally, and agreed that chemical weapon use by Syrian President Syrian President Bashar Assad's forces would merit a "serious response," a spokesperson for the prime minister said in a statement.
US Secretary of State John Kerry spoke to Syrian foreign Walid Moualem on Thursday and told him the Damascus government should have let UN inspectors have access to the site of an alleged gas attack, the State Department said on Saturday.
Kerry called "to make clear that if, as they claimed, the Syrian regime has nothing to hide, it should have allowed immediate and unimpeded access to the site rather than continuing to attack the affected area to block access and destroy evidence," a State Department official said.
"The secretary further emphasized ... that he had received full assurances from Free Syrian Army commanders that they would ensure the safety of UN investigators into the targeted areas," the official said.
Kerry, who participated remotely in a White House meeting on a potential US response to the alleged use of chemical weapons in Syria, made a round of diplomatic calls on Saturday to his counterparts in Saudi Arabia, Jordan and Turkey, the official said.
"In all these calls, the secretary emphasized the importance of quickly determining the facts and underscored the seriousness and gravity of any chemical weapons use," the official said.
Americans gun-shy about US intervention in Syria
According to a Reuters/Ipsos poll, Americans strongly oppose US intervention in Syria's civil war and believe Washington should stay out of the conflict even if reports that Syria's government used deadly chemicals to attack civilians are confirmed.
About 60 percent of Americans surveyed said the United States should not intervene in Syria's civil war, while just 9 percent thought President Obama should act.
More Americans would back intervention if it is established that chemical weapons have been used, but even that support has dipped in recent days - just as Syria's civil war has escalated and the images of hundreds of civilians allegedly killed by chemicals appeared on television screens and the Internet.
The Reuters/Ipsos poll, taken August 19-23, found that 25 percent of Americans would support US intervention if Assad's forces used chemicals to attack civilians, while 46 percent would oppose it. That represented a decline in backing for US action since August 13, when Reuters/Ipsos tracking polls found that 30.2 percent of Americans supported intervention in Syria if chemicals had been used, while 41.6 percent did not.
Taken together, the polls suggest that so far, the growing crisis in Syria, and the emotionally wrenching pictures from an alleged chemical attack in a Damascus suburb this week, may actually be hardening many Americans' resolve not to get involved in another conflict in the Middle East.
The results - and Reuters/Ipsos polling on the use-of-chemicals question since early June - suggest that if Obama decides to undertake military action against Assad's regime, he will do so in the face of steady opposition from an American public wary after more than a decade of war in Iraq and Afghanistan.