Defense Secretary Chuck Hagel said Sunday the US military was ready to take action against the Syrian regime if ordered, but stressed that Washington was still evaluating claims of a chemical weapons attack.
"President Obama has asked the Defense Department to prepare options for all contingencies. We have done that," Hagel told reporters in the Malaysian capital Kuala Lumpur.
"Again, we are prepared to exercise whatever option, if he decides to employ one of those options."
He said the US and its allies were assessing intelligence on allegations that President Bashar al-Assad's forces unleashed chemical weapons in an attack near Damascus last week as he battles an uprising that began in March 2011.
"I wouldn't go further than that, until we have more intelligence based on facts," Hagel said.
Hagel spoke after a meeting with his Malaysian counterpart, Hishammuddin Hussein, as he started a week-long Southeast Asia tour to stress Washington's much-touted renewed focus on the Asia-Pacific region.
But his attention has been diverted by crises in Syria and Egypt, where security forces have cracked down on supporters of ousted Islamist president Mohamed Morsi.
Hagel phoned Egypt's army chief from Kuala Lumpur to appeal for a peaceful resolution of political conflicts there, and has been in touch with top US national security advisers on Syria.
Hagel reiterated the US military had presented a range of military options to President Barack Obama over the apparent chemical attack that has sparked international revulsion.
On his flight to Malaysia from Hawaii, he told reporters the American military was moving forces into place as needed, amid speculation Washington might opt for cruise missile strikes to punish Assad's regime.
Obama and British Prime Minister David Cameron appeared to move closer to pinning blame on Assad's forces.
A Downing Street statement said the US and British leaders "are both gravely concerned by... increasing signs that this was a significant chemical weapons attack carried out by the Syrian regime against its own people".
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The Syrian government and rebel forces have accused each other of using chemical weapons.
Doctors Without Borders said 355 people had died of "neurotoxic" symptoms stemming from Wednesday's incident.
The United Nations says more than 100,000 people have been killed in the Syrian uprising.
Hagel later gave a speech in which he underlined Washington's bid to rebalance America's strategic focus towards the Asia-Pacific.
The tilt to Asia is seen as based in part on the region's growing economic importance and to counterbalance the expanding military might of China.
Beijing has been accused of raising tensions by aggressively asserting its disputed claim to virtually all of the South China Sea.
Hagel said Washington was "troubled" by a series of resulting confrontations, calling for restraint and a regional agreement on a set of rules to avoid conflict at sea.
China has long been accused of dragging its feet on the idea but this year has agreed to meet Southeast Asian countries to discuss it.
The Pentagon is offering help to regional states in the form of material and training as they try to better monitor their waters.
A senior defence official travelling with Hagel rejected the "myth" that Pentagon budget cuts imperil the Asia "pivot".
"We have adequate means to support this strategy and to do so for the foreseeable future," the official said, speaking on condition of anonymity.
The United States was increasing the number of naval ships in the Asia-Pacific and pursuing agreements to allow vessels, aircraft and troops to rotate through key ports and airfields while avoiding permanent American bases, the official said.
After his two-day stop in Malaysia, Hagel heads to Indonesia and then Brunei for a regional defence gathering that will include China.