The US held a flurry of diplomatic talks on Thursday to discuss possible new action against the Syrian government amid mounting international concern over alleged chemical weapons attacks.

Though it stressed it had still not yet seen conclusive proof of chemical weapon use, the US State Department revealed that secretary of state John Kerry had held seven calls with overseas counterparts on Thursday, and had taken part in a national security council meeting at the White House.

The British Foreign Office confirmed Kerry had spoken to William Hague. A spokesman declined to comment on the contents of the call.

Washington is split over how to respond to the latest attack, which it believes may have killed between 1,000 and 1,800 people. Military leaders such as John Dempsey, the chairman of the joint chiefs of staff, have urged caution, for fear of becoming further embroiled in a Middle East conflict when it is unclear whether the rebels would back US interests.

"Syria today is not about choosing between two sides but rather about choosing one among many sides," Dempsey said in the letter dated 19 August to Representative Eliot Engel. "It is my belief that the side we choose must be ready to promote their interests and ours when the balance shifts in their favor. Today, they are not."