United States Defense Secretary Chuck Hagel says the US military is ready to act immediately should President Barack Obama order action against Syria over a chemical weapons attack.
Mr Hagel said the United States has moved assets to be able to fulfill whatever option Mr Obama wishes to take.
In a BBC interview, he said it is increasingly clear to him that the Syrian government was responsible for the chemical attacks on civilians.
White House spokesman Jay Carney later said that a separate report on chemical weapons use being compiled by US intelligence agencies would be published this week.
US Secretary of State John Kerry has said there is "undeniable" proof that Syria used chemical weapons.
The Arab League also holds the Syrian government fully responsible.
President Francois Hollande says France is "ready to punish" whoever was behind the attack.
The British Parliament is to be recalled to discuss possible responses. Prime Minister David Cameron said the world cannot ignore the act, but any military action must be specific, legal and designed to deter future use of chemical weapons.
Syrian foreign minister Walid Al Muallem said the claims by Western governments were lies designed to serve the interests of Israel and al-Qaeda.
He said Syria will defend itself by all means possible if attacked.
Russia, Iran and China have stepped up their warnings against intervention. Moscow said any such action would have "catastrophic consequences".
The UN says its team of weapons inspectors in Damascus has delayed making a second visit to the scene of the attacks, which occurred on 21 August.
A convoy carrying the inspectors came under fire from unidentified gunmen on Monday.