Cameron will decide later on Tuesday whether to recall lawmakers from their summer break to debate a possible military intervention in the wake of an alleged chemical weapons attack near Damascus last Wednesday, Downing Street said.

"We are continuing to discuss with our international partners what the right response should be, but, as part of this, we are making contingency plans for the armed forces," Cameron's spokesman said.

The prime minister will continue talks with other world leaders to agree a "proportionate response" to the gas attack, which the United States, Britain and France say was committed by Syrian government forces.

"This is about deterring the use of chemical weapons," the British spokesman said