Russian defence ministry spokesman Igor Konashenkov said the military had "proof that testifies to the direct participation of Britain in the organising of this provocation in Eastern Ghouta."
He said Britain had told the White Helmets, who act as first responders in rebel-held areas, to fake the suspected chemical attack in the town of Douma.
He said the attack was staged on April 7 to coincide with military action by Syrian government forces, after the rebel group Jaish al-Islam that long controlled Eastern Ghouta carried out shelling of Damascus from April 3 to 6.
Russia has repeatedly accused rebels of staging or spreading rumours of chemical attacks, but the involvement of Britain is a new claim.
In March Russia's General Staff said that rebels were planning a "provocation" in Eastern Ghouta with women and children set to play victims of a chemical attack.
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