The global chemical arms watchdog on Monday opened emergency talks on the suspected poison gas attack in the Syrian town of Douma, diplomatic sources told AFP.

The meeting has "just started," said one source as the closed-door talks went into session.

Earlier the British, Russian and French ambassadors were all seen arriving at the headquarters of the Organisation for the Prohibition of Chemical Weapons (OPCW) in The Hague.

The OPCW has 192 members, and Monday's governing executive council meeting of 41 states was called by its chairman, Bangladeshi ambassador Sheikh Mohammed Belal, "to discuss the alleged use of chemical weapons" in Syria.

An OPCW fact-finding team is also in Syria to probe the alleged attack on Douma in which 40 people died.