Britain and France have angrily accused Russia of a "despicable" stunt after Moscow brought a series of alleged witnesses to what it claims was a "staged" Syrian gas attack before the international chemical weapons watchdog.

Russian diplomats will bring a group of Syrians to the international chemical weapons watchdog who the Russians claim were filmed in "staged videos" of an alleged chemical attack on the town of Douma earlier this month.

Mustard gas was used by insurgents in Syria in an attack that likely killed an infant, the Organisation for the Prohibition of Chemical Weapons (OPCW) has confirmed.