"We have moved assets in place to be able to fulfil and comply with whatever option the president wishes to take," Mr Hagel told the BBC.
US Secretary of State John Kerry has said there is "undeniable" proof that Syria had used chemical weapons.
The UK Parliament is to be recalled on Thursday to discuss possible responses.
Britain is considering military responses to the attack.
Prime Minister David Cameron, who has cut short his holiday and returned to London, said MPs would vote on a "clear motion" on the crisis.
Syria's allies, Russia and China, have stepped up their warnings against military intervention in Syria, with Moscow saying any such action would have "catastrophic consequences" for the region.
Meanwhile Syrian Foreign Minister Walid Muallem said he rejected "utterly and completely" claims that Syrian forces had used chemical weapons. » | Tuesday, August 27, 2013
