Russia said it would deliver its response to Britain’s decision to expel four diplomats later today.
As well as the expulsions, Britain has withdrawn co-operation on easing visa regulations in response to Moscow’s refusal to extradite the prime suspect in the polonium 210 killing of Alexander Litvinenko.
British prosecutors have accused Russian businessman Andrei Lugovoy, a former intelligence officer, of carrying out the poisoning and have emanded his extradition to face trial in Britain.
Russia has refused, quoting a constitutional ban on extraditing its own citizens.
Russian media described Britain’s response as a declaration of diplomatic war.
British Prime Minister Gordon Brown said Britain will make “no apologies” for expelling the Russians.