Syrian Deputy Foreign Minister Faisal Mekdad also told the BBC that armed groups backed by America had used chemical weapons - not Syrian troops. 

 

The US earlier said it had evidence that Damascus had used the nerve agent sarin in a deadly attack last week.

 

President Barack Obama has vowed¹ punitive² action but wants Congress to vote on the issue first.

 

US lawmakers are due to reconvene（再召开） next week, and White House officials have said they believe they will support the president.

 

Campaigning to convince people and politicians that military intervention³ is the right way forward has already begun in America, correspondents say.

 

But by putting off an attack and seeking congressional approval, President Obama has taken the biggest gamble of his presidency⁴, the BBC's North America editor Mark Mardell says. 

 

He adds that if Congress does not back him, it would be disastrous⁵ for the president and his decision to call for a vote would look foolish.

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