US - The United States and its allies geared up on Tuesday for a probable military strike against Syria that could come within days and would be the most aggressive action by Western powers in the Middle Eastern nation's two-and-a-half-year civil war.
Western envoys have told the Syrian opposition to expect a military response soon against President Bashar al-Assad's forces as punishment for a chemical weapons attack last week, according to sources who attended a meeting with the rebel Syrian National Coalition in Istanbul.
Amid a quickening drum beat of preparations, US Defence Secretary Chuck Hagel said American forces in the region were "ready to go" if President Barack Obama gave the order.
Obama - long reluctant to intervene in the Syrian conflict - worked to solidify allied support, including calling the leaders of Britain and Canada, while US intelligence agencies assembled what they are sure to say is final confirmation of the Syrian government's culpability for Wednesday's poison gas attack near Damascus.
White House spokesman Jay Carney said it would "fanciful" to think that anyone other than Assad's forces was behind the large-scale chemical attack, which activists said killed hundreds of people as they slept.
"There is no doubt who is responsible for this heinous use of chemical weapons in Syria: the Syrian regime," Vice President Joe Biden said at a speech in Houston to the American Legion, a military veterans' group.
Obama has yet to make a final decision on the US response, Carney said, but left little doubt that it would involve military action. He insisted, however, that Washington was not intent on "regime change," signalling that any military strikes would be limited and not meant to topple Assad.
The British military was also drafting plans. Prime Minister David Cameron, anxious, like Obama, not to emulate entanglements in wars in Afghanistan and Iraq that beset their predecessors, said any strikes would be "specific" so as not to drag the allies deeper into Syria's civil war.