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.
He said Russian specialists and aid workers had visited the area. Rebel fighters have started leaving the town under a surrender deal.
Medical sources say dozens were killed in Saturday’s alleged attack but numbers are impossible to verify.
The US and France threatened a “joint, strong response” to the alleged attack.
The United Nations Security Council is to discuss the allegations later on Monday.
The Russian denial came hours after a deadly attack on a Syrian military airport, which Moscow and the Syrian government blamed on Israel.
Missiles hit the Tiyas airbase, known as T4, near the city of Homs. Observers say 14 people were killed.
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 if the strike has anything to do with the suspected chemical attack.