White House questions Syrian weapons claim The White House played down reports on Tuesday that Syria used chemical weapons on its own citizens during a December attack on rebels in the city of Homs. A report by Foreign Policy, the magazine and website, said a secret US state department cable had concluded that the Syrian government forces likely used a form of poison gas during the December 23 attack on Homs. Tommy Vietor, a spokesman for the National Security Council, said in a statement that reporting about the incident in Homs was not "consistent with what we believe to be true about the Syrian chemical weapons programme." If confirmed, the report would be very significant because it would represent dramatic escalation in the level of violence in Syria and because the Obama administration has said that the use of chemical weapons is a "red line" that would lead to direct intervention in the two year-long conflict. According to Foreign Policy, US diplomats conducted an investigation into the December 23 attack in Homs, talking to doctors, activists and defectors, before preparing the cable. The report quoted an Obama administration official who has seen the document as saying: "We can't definitely say 100 per cent, but Syrian contacts made a compelling case that Agent 15 [a chemical weapon] was used in Homs on December 23," the official said. The report follows widespread speculation that some form of chemical weapon had been used during the attack, including videos which were circulated on YouTube at the time by activists. Speaking in August last year, President Barack Obama said that the use of chemical weapons was a "red line" that would provoke a US military response. "We have been very clear to the Assad regime - but also to other players on the ground - that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilised," he said. That would change my calculus; that would change my equation. Mr Vietor repeated the same point on Tuesday. "The President was very clear when he said that if the Assad regime makes the tragic mistake of using chemical weapons, or fails to meet its obligation to secure them, the regime will be held accountable," he said. The political fallout could also be influenced by the nature of the poisonous gas used. Agent 15, also sometimes known as BZ, is much less deadly than most other known chemical weapons. General Martin Dempsey, chairman of the joint chiefs of staff, admitted last week that it would be almost impossible to prevent the Syrian government from using chemical weapons if it wanted to. "The act of preventing the use of chemical weapons would be almost unachievable," he said.