Syria gas attack claims: Evidence 'compelling', says expert

Evidence apparently corroborating reports of chemical weapon attacks in Syria in recent weeks is "compelling" but incomplete, an expert has told the BBC.

Hamish de Bretton-Gordon, a former commanding officer at the UK's Joint Chemical Biological Radiological Nuclear Regiment, said of doctors who told the BBC they treated victims: "I gauge that they're not making it up."

A BBC correspondent who visited the northern town of Saraqeb was told by eyewitnesses that government helicopters had dropped at least two devices containing poisonous gas.

The government has vehemently denied claims it has used chemical agents.

Mr de Bretton-Gordon told the BBC's Ian Pannell that to know "whether red lines have been crossed", the UN would need to see "forensically collected samples".