Iran has warned against "military intervention" in Syria as Bashar al Assad's regime was accused by Western leaders of massacring 1,300 people with chemical weapons.Tehran also said it believes the alleged gas attack in Ghouta, an eastern suburb of Damascus, was carried out by rebel forces.
Abbas Araqchi, Iran's foreign ministry spokesman, said: "There is evidence that this action was carried out by terrorist groups.
"The concurrence of the use of these weapons with the presence of UN inspectors is itself an indication that there are hands at work to accuse the Syrian government of using these weapons and help the conflict and crisis to continue."
He spoke out after Syrian state TV ran footage of "barrels filled with highly dangerous toxic and chemical agents" as well as gas masks, saying they were only a small sample of what had been unearthed in rebel positions.
The UN's disarmament chief Angela Kane has arrived in the capital to push the Assad regime to allow weapons inspectors to visit the area to assess whether a chemical atrocity has been carried out.
Her visit comes as America boosted its military capacity in the region to give what the US has called "a range of options available".
President Barack Obama is meeting his national security team today to discuss the crisis.
The New York Times quoted a senior US administration official as saying Washington was looking at NATO's aerial strikes in Kosovo in 1999 as a blueprint for action against Syria without a UN mandate.
US Defence Secretary Chuck Hagel said Mr Obama had asked the Pentagon to prepare military options for Syria.
He declined to give details on specific force movements, but the AP news agency said a fourth warship has been sent to the eastern Mediterranean Sea.
Three other destroyers are currently deployed there - the USS Gravely, USS Barry and USS Ramage.
All four warships are equipped with Tomahawk cruise missiles allowing the Pentagon to act rapidly if a military strike is ordered against Syria.
French Foreign Minister Laurent Fabius piled pressure on Damascus, saying the regime carried out a "chemical massacre".
On Friday, Russia, a major ally of the Syrian government, joined calls for a swift probe into the alleged chemical attack.
British Foreign Secretary William Hague said there was little chance the attack had been carried out by rebels.
He said: "The only possible explanation of what we have been able to see is that it was a chemical attack and clearly many, many hundreds of people have been killed, some of the estimates are well over 1,000.
"I know some people in the world would like to say this is some kind of conspiracy brought about by the opposition in Syria - I think the chances of that are vanishingly small."
The Assad regime has denied it has used chemical weapons, calling the allegations "absolutely baseless".
The UN says more than 100,000 people have been killed in Syria since the conflict began in March 2011, and millions have fled the country.