British officials say the Russian order to reduce Britain's diplomatic presence in Moscow is "regrettable" but had been anticipated.
Russia's Foreign Ministry says it has ordered Britain to reduce the number of its diplomats in Moscow to the level that Russia has in London.
A Foreign Office statement released Friday said the Russian action "doesn't change the facts" of the nerve-agent attack on ex-spy Sergei Skripal and his daughter.
It says there is no alternative to the conclusion that the Russian state was to blame for the attempted "assassination of two people on British soil."
The Foreign Office says Russia is "in flagrant breach of international law and the Chemical Weapons Convention."
Officials refuse to discuss how many diplomats might have to be removed to comply with the Russian order.
