Russian diplomats called the decision "immoral," warned of an inevitable political backlash, and pledged an appropriate retaliation after U.K. Foreign Secretary David Miliband announced the move.
"We have chosen to expel four diplomats, four particular diplomats, in order to send a clear and proportionate signal to the Russian government about the seriousness of this case," Miliband told parliament. The move is a response to Russia's refusal to extradite agent-turned-businessman Andrei Lugovoi for trial in the U.K.
The new foreign secretary also said negotiations between Russia and the European Union over facilitating the visa regime would be suspended and visa restrictions introduced for Russian officials. A spokesman for the British Embassy in Moscow clarified that the restrictions would not concern tourists or other ordinary citizens.
The Russian Foreign Ministry described Miliband's announcement as "a carefully choreographed action" that would inflict serious damage to bilateral relations. Ministry spokesman Mikhail Kamynin also said Russia was ready to cooperate with Britain on the Litvinenko case.
Lugovoi, who met Litvinenko on the day he fell ill in London, told journalists that London's decision to expel Russian diplomats was a clear attempt to politicize the case.
"These decisions show that the Litvinenko case was politically motivated from the very start," Lugovoi said, while also maintaining his innocence. "Nobody invited me to Britain - I faced the charges in absentia, and nobody gave me any chance to defend myself."
Litvinenko died in a London hospital in November 2006. British experts said they had discovered radioactive isotope polonium-210 in his body, but published no official autopsy results. In a deathbed note, purportedly written by Litvinenko, who received British citizenship shortly before his death, he blamed President Vladimir Putin for his murder, an allegation the Kremlin dismissed.
Early last week, British prosecutors said they had received Russia's official refusal to extradite Lugovoi, which cited the Russian Constitution as saying Russian citizens could not be handed over to other countries, and proposed trying Lugovoi in Russia if Britain provides sufficient evidence. But a spokesman for British Prime Minister Gordon Brown said the country's authorities could not be sure a Russian trial would be unbiased.
In his address to parliament, Miliband also urged Russia to consider changing its Constitution to make international cooperation in law more efficient, including in the extradition of criminal suspects.
Russia in turn wants Britain to extradite two of its own suspects, fugitive tycoon Boris Berezovsky and Chechen emissary Akhmed Zakayev. Berezovsky is accused of fraud and a coup attempt, while Zakayev is facing terrorism charges. Both have been granted British passports.
Russian diplomatic spokesman Kamynin said: "We have the impression that British authorities are trying to justify their refusal to cooperate with Russian law enforcement officials on the extradition of Zakayev and Berezovsky, against whom we have undeniable evidence of terrorism."