The United States has evidence that Bashar al-Assad used sarin gas in the devastating chemical weapons attack that killed more than 1,400 people last month, the US secretary of state announced on Sunday, as a French report laid bare the extent of Syria's toxic arsenal.
Describing the use of sarin as a "very important new development" John Kerry piled pressure on Congress to back Barack Obama after the president's decision to hold a vote when they return.
Yesterday, a report by France's intelligence agencies said that Assad's regime had amassed more than 1,000 tons of chemical weapons, including sarin, mustard gas and VX gas and has the technology to deliver them hundreds of miles.
The study, by the Direction Generale de la Securite Exterieure (DGSE), published in a French Sunday newspaper, said Damascus had "one of the world's largest stocks of operational chemical weapons".
It said some of the weapons had been stockpiled for almost 30 years and that Syria's chemical arsenal was "particularly massive and diverse", comprising several hundred tons of Yperite, a substance similar to mustard gas; several hundred tons of sarin and dozens of tons of VX, the most toxic of all chemical agents.
The report said Assad and the most influential members of his "clan" were the only ones able to give the order to use chemical weapons. It also said the Syrian president had an arsenal of scud missiles that could carry chemical weapons 310 miles (500km) and bombs capable of delivering up to 65 gallons (300) litres of toxic agents.
Yesterday Kerry linked Assad to "Adolf Hitler and Saddam Hussein" as the only leaders to breach an almost century-old taboo against chemical weapons. Kerry said he refused to believe that the US Congress would allow the Syrian regime to get away with murder.
"I can't contemplate that the Congress would turn its back on all of that responsibility and the fact that we would have in fact granted impunity to a ruthless dictator to continue to gas his people," he said on Fox News. "Those are the stakes."
The use of sarin, which Kerry said was detected in soil and blood samples obtained by the US from first responders, is significant because the nerve agent is proscribed as a weapon of mass destruction under UN resolution 687. Kerry spoke out after Obama's unexpected announcement on Saturday that he was holding off strikes against Syria and would ask Congress to back attacks aimed at "deterring and degrading" Assad's ability to use chemical weapons.
Kerry fought off criticism from home and abroad that Obama had made himself look weak and indecisive, telling CNN the president retained the right to use force even if he lost the vote but "believes that we are stronger as a nation when we act together". Although Obama has the support of the Democrat-controlled Senate, analysts said yesterday that his managers will have to work hard to win over the Republican-controlled House of Representatives.
Leaders said a vote would be held "no later" than the week of September 9. A senior Syrian official who defected to Britain claimed yesterday that the Foreign Office had been instrumental in helping to prevent a chemical weapons attack last year after seeing preparations being made. Khaled al-Ayoubi, who defected in July 2012, said he had delivered an ultimatum to the regime at the Foreign Office's request.