The decision to expel the Russian diplomats was taken after Russia has refused to extradite murder suspect Andrei Lugovoi to face trial in Britain.

A former KGB agent, Andrei Lugovoi was named by the U.K. Crown Prosecution Service as the prime suspect in the murder of Kremlin critic Alexander Litvinenko.

Litvinenko, 43, died in London in November after being poisoned by radioactive polonium-210. UK requested Lugovoi extradition so he can stand the trial, but Russia refused to comply.

“A U.K. citizen has suffered a horrifying and lingering death,” Foreign Secretary David Miliband told Parliament in London on Monday.

Miliband said that according to the police Lugovoi had offered tea to Litvinenko and that he later "suffered a horrifying and lingering death in front of his family. His murder put hundreds of others, residents and visitors, at risk of radiation contamination."

The Russian government condemned the move as "provocative" and "immoral" and said it would have "the most serious consequences for Russian-British relations as a whole."

According to the British news service BBC, Prime Minister Gordon Brown said there were "no apologies" for the expulsions, explaining that if "there is no forthcoming co-operation (from Russia), then action has to be taken."

Also today leading Russian newspapers reacted by calling Britain’s decision a diplomatic war.

“The new British prime minister has declared war on Russia — a diplomatic one,” the pro-Kremlin daily Izvestia said. “It won’t be long before an “appropriate response’ from Moscow. But what does Britain need a “second front’ for when it hasn’t finished dealing with the terrorists who have declared a jihad against it?”

According to the Russian Foreign Ministry's press service, Deputy Foreign Minister Alexander Grushko will read a prepared statement at 5.30 p.m. Moscow time as response to Britain’s decisions.

Russia will order the expulsion of U.K. diplomats in Moscow and restrict the issuing of visas to British citizens, Russian newspaper Kommersant reported today, citing an unidentified Foreign Ministry official.

Meanwhile, Litvinenko's widow Marina issued a statement thanking the British government for its stand and urging the Russia to cooperate.

"It makes me proud to be a UK citizen because I can see that my strong faith in the British authorities was well founded and that they too share my determination," she said.

The Russian daily Vremya Novostei on Tuesday reported that economic experts were playing down any possible negative repercussions from the affair on British-Russian economic relations, quoting one investment banker as saying the purported problems with business interests were "fudged."