American forces are “ready” to launch strikes on Syria if President Barack Obama chooses to order an attack, US Defense Secretary Chuck Hagel says.
“We have moved assets in place to be able to fulfill and comply with whatever option the president wishes to take,” Mr Hagel told the BBC.
US Secretary of State John Kerry has said there was “undeniable” proof that Syria had used chemical weapons.
The UK is also preparing contingency plans for military action in Syria.
British Prime Minister David Cameron has cut short his holiday and returned to London to deal with the Syrian 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.
His government has blamed rebel fighters for the suspected chemical attack, which took place on 21 August near the Syrian capital Damascus, and reportedly killed more than 300 people.
On Monday, United Nations chemical weapons inspectors were fired on while investigating one of the five alleged attack sites around Damascus.