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The diplomatic confrontation between Britain and Russia over the murder of Alexander Litvinenko is showing no sign of quieting. Litvinenko was the Russian exile who was poisoned with the rare radioactive isotope polonium-210 in London last November.

Moscow has yet to respond to Britain's decision to expel four Russian diplomats. Those expulsions were in retaliation for Russia's refusal to extradite the prime suspect in Litvinenko's murder.

Today, another Russian exile in Britain, the Kremlin critic Boris Berezovsky, held a news conference in London. He was one of those who would accuse Russian President Vladimir Putin of being behind Litvinenko's murder and he told the press there that there had been a plot to kill him, too.

NPR's Rob Gifford reports.

ROB GIFFORD: The Russian government said yesterday that it was weighing up its response to the British expulsions. But in the meantime, British media have been abuzz with the allegations of billionaire Boris Berezovsky, one of the so-called oligarchs who made a fortune after the collapse of the Soviet Union.

Berezovsky has been a consistent thorn in Moscow's side. He fled Russia and was given asylum in Britain in 2003. At the news conference today, he claimed that three months ago, his contacts in Moscow warned of a specific threat against him.

Mr. BORIS BEREZOVSKY (Exiled Russian Billionaire): They said that someone who knows you will travel to London, he will go to meet him and he will simple kill you and will not try to hide, because he explains that it's just business reason. He had problem with me in business and he decide to kill me. And he -in this case, according to British law, he will get about 20 years. He will spend 10 years in jail, will be released, will have a lot of money and his family, will become hero of Russia. And this was the plan.

GIFFORD: Berezovsky said three weeks ago, the British police got wind of a plot and advised him to leave Britain for a week, which he did. Police confirmed today that a man was arrested on June 21st in connection with the plot to kill Berezovsky, but was released two days later without charge. The Russian ambassador in London, Yuri Fedotov, has denied allegations that the Russian government was involved, and accused the British government of leaking the story.

Mr. YURI FEDOTOV (Russian Ambassador to the United Kingdom): I'm not aware of any official information from any official sources that could corroborate this story. A possible explanation why this leakage happened in the middle of the situation when the British government has decided to expel Russian diplomats, and it appears now that in order to support these measures, to explain to the British public opinion why it has been done, this story was take out by the press.

GIFFORD: Fedotov said Britain would not have to wait long for Russia's response to the expulsion of the diplomats. It may take place today or tomorrow, he said.

Rob Gifford, NPR News, London. Transcript provided by NPR, Copyright NPR.