Britain said the West could act even without full UN Security Council backing.

Washington and its allies have pointed the finger of blame at Assad for the alleged attack, the latest atrocity in a conflict that has claimed the lives of more than 100,000 people since March 2011.

Assad, in an interview with a Russian newspaper published on Monday, angrily denied the accusations as an "insult to common sense" and said any military action was doomed to failure.

"The US faces failure just like in all the previous wars they waged," he said.

A senior Syrian security official told AFP the government was ready to face "all scenarios".

"Western threats of strikes against Syria are part of the psychological and political pressure against Syria, but in any case we are ready to face all scenarios," the official said.

Russian Foreign Minister Sergei Lavrov warned his US counterpart John Kerry of the "extremely dangerous consequences of a possible new military intervention for the whole Middle East and North Africa region".

Syrian authorities had approved the UN inspection of the site in Ghouta east of Damascus on Sunday, but US officials said it was too little, too late, arguing that persistent shelling there in recent days had "corrupted" the site.

Mortar shells also hit a mosque in the center of Damascus on Monday, the Syrian news agency SANA said, blaming "terrorists".

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