Russian Foreign Minister Sergei Lavrov has said no evidence has been found of a chemical weapons attack in Syria's formerly rebel-held town of Douma.

Medical sources say dozens were killed in Saturday's alleged attack but numbers are impossible to verify.

Mr Lavrov said Russian specialists and aid workers had visited the area, which rebel fighters have started leaving under a surrender deal.

The US and France have threatened a "joint, strong response".

The claim from Russia - which has intervened militarily in Syria in support of the government - came after videos shot by rescue workers on Saturday showed lifeless bodies of men, women and children with foam at their mouths.

The Syrian-American Medical Society said more than 500 people were brought to medical centres in Douma, in the Eastern Ghouta region, near the capital Damascus, with symptoms "indicative of exposure to a chemical agent", including breathing difficulties, bluish skin, mouth foaming, corneal burns and "the emission of chlorine-like odour".

The UN Security Council is to discuss the allegations later on Monday.

Mr Lavrov spoke hours after a deadly attack on a Syrian military airbase, which Moscow and the Syrian government blamed on Israel.

Missiles hit the Tiyas facility, known as T4, near the city of Homs. Fourteen people are said to have been killed, including three Iranians.

Israel, which has previously hit Syrian targets, has not commented. Syria initially blamed Washington for the strike, but the US, UK and France have all denied involvement.

It is unclear whether the strike had anything to do with the suspected chemical attack.

Read more on bbc.com.