Washington - US President Barack Obama and British Prime Minister David Cameron inched closer on Saturday to attributing blame for a massive chemical weapons attack near Damascus to Bashar al-Assad's armed forces.
A Downing Street statement said the US and British leaders "are both gravely concerned by... increasing signs that this was a significant chemical weapons attack carried out by the Syrian regime against its own people."
"The fact that President Assad has failed to co-operate with the UN suggests that the regime has something to hide," it added, noting that "significant use of chemical weapons would merit a serious response from the international community."
Obama and Cameron spoke by phone and will "continue to consult closely" regarding the reported massacre, a more circumspect White House statement said, after the US president met with his top security aides.
The Syrian government and its foes, meanwhile, accused each other of using chemical weapons, as Doctors Without Borders said 355 people had died of "neurotoxic" symptoms stemming from Wednesday's incident, with thousands more being treated in hospital.
If confirmed, the attack would be the deadliest use of chemical agents since Saddam Hussein gassed Iranian troops and Kurdish rebel areas in northern Iraq in the 1980s.