Russia expelled four British diplomats Thursday and suspended cooperation with London on fighting terrorism, as a bitter row over Moscow's refusal to extradite a murder suspect escalated.

The Kremlin said Russia had been forced into a "proportionate response" after Britain threw out four Russian diplomats earlier this week.

Foreign Ministry chief spokesman Mikhail Kamynin told reporters the British ambassador had been summoned and handed a note about "the unfriendly actions of Britain towards Russia".

"Four British Embassy staff in Moscow are now persona non grata and they should leave the territory of the Russian Federation within 10 days," Kamynin said.

British Ambassador to Moscow Tony Brenton leaves Russia's Foreign Ministry in Moscow July 19, 2007.

Britain called the expulsions "completely unjustified" and said it was disappointed Moscow had not signaled any fresh cooperation in the case of Alexander Litvinenko, a former Russian security agent murdered in London last year.

The United States and the European Union both weighed in with declarations of support for Britain and asked Russia to reconsider its refusal to cooperate. Moscow says its constitution prohibits the extradition of its citizens.

British prosecutors have charged Andrei Lugovoy, a former KGB bodyguard, with killing Litvinenko by spiking his tea with lethal radioactive polonium in a London hotel. Lugovoy denies the allegations.

Russia will also stop issuing visas to British officials and cease cooperation with London in the war on terror, Kamynin said, adding that Russia's response was the "minimum necessary".

Analysts in Moscow said Russia had reacted with relative restraint to Britain's moves and noted official statements emphasizing a desire not to affect business ties between the two nations, which are booming.

(China Daily via agencies July 20, 2007)