Britain has said Russia's military build-up in Syria reinforces President Bashar Assad and increases Moscow's "moral responsibility in the crimes committed by the regime".
"Russia's military build-up complicates the situation," Foreign Secretary Philip Hammond told the French daily Le Monde
in an interview after talks with his French and German counterparts in Paris on Thursday night.
"Assad must go, he can't be part of Syria's future," Hammond added, according to Le Monde
's French translation. "If we reach a deal on a transition authority and Assad is part of it, then it will be necessary to talk with him in his capacity as an actor in this process."