Alexander Litvinenko, the former KGB agent who died Thursday in a London hospital, had a toxic radioactive substance in his body, according to British authorities. Doctors had initially thought he had been poisoned by a heavy metal known as thallium.
In a statement dictated from his deathbed, Litvinenko, who became a fierce Kremlin critic, blamed Russian President Vladimir Putin for his death. Putin denied any Kremlin involvement.
At a news conference, a letter written by Litvinenko before he died was read out by his friend Alex Goldfarb. It was addressed directly to Putin.
"You have shown yourself to be as barbaric and ruthless as your most hostile critics have claimed," the letter said. "You have shown yourself to be unworthy of your office and of the trust of civilized men and women."
Litvinenko had been investigating the murder of journalist Anna Politkovskaya in Moscow when he fell ill on Nov. 1 after meeting with two Russians in London, and then eating at a sushi restaurant.
Many dissidents say Litvinenko was poisoned by the Kremlin. But speaking to reporters Friday at a summit with European Union leaders in Helsinki, Putin denied any involvement.
"The medical statement of the British physicians doesn't say that this was the result of violence," Putin said. "This was not a violent death. So there are no grounds for speculation of this kind."
Putin said Russia "will offer all necessary help to the investigation."
Britain's Health Protection Agency said the radioactive element polonium-210 had been found in Litvinenko's urine. The agency's chief executive said that the high level indicated Litvinenko "would either have to have eaten it, inhaled it or taken it in through a wound."
The authorities said they had also found traces of radiation at the sushi bar in central London where Litvinenko ate the day he became sick and at the hotel where he met two Russians that same day.
The British government says it has raised what it called the "serious matter" of Litvinenko's death with Moscow.
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