"It is a pity that tragic events like death have been used for political provocations," Vladimir Putin told a news conference following a Russia-EU summit in Helsinki, at which he had to field questions on the assassination story.
Alexander Litvinenko, a former Russian intelligence officer and defector, died early Friday. Western media has circulated the deathbed note of Litvinenko, known as a fierce critic of the Kremlin, in which he accused Vladimir Putin of orchestrating his death.
"British doctors did not indicate in their statement that it was a violent death. This means there are no grounds for this kind of speculation," Putin said.
The president said he doubted the veracity of the deathbed note, saying he found it strange that it was only published after Litvinenko's death. The president suggested its authors, unable to save Litvinenko, resorted to the trick to keep the story going.
"Those who did it [concocted the note] are not God, and Mr. Litvinenko is unfortunately not Lazarus," Putin said, referring to a Biblical character raised from the dead by Jesus.
Litvinenko, 43, a former officer of the Federal Security Service, was admitted to a London hospital three weeks ago, diagnosed with acute poisoning. Doctors at London's University College Hospital found traces of radioactive polonium-210 in the deceased's body earlier Friday.
Litvinenko lost all his hair and was unable to eat for 18 days. Doctors said his bone marrow was badly damaged, depriving his body of white blood cells.
Litvinenko defected in 2000, emigrating to the United Kingdom with his wife and son. He lived their as a political emigre and received citizenship in October 2006.
A close associate of Russia's fugitive oligarch Boris Berezovsky, Litvinenko said in an interview with The Sunday Times newspaper he believed the poisoning was a murder plot to avenge his defection. The Kremlin has dismissed the accusation as nonsense.
Putin said he hopes British investigators will not encourage ungrounded speculation conducive to political scandals and said Russian authorities are willing to provide assistance in the investigation.
Litvinenko was also reportedly investigating the murder in October of Russian journalist Anna Politkovskaya, known for her criticism of the Kremlin.
His death and the murder of Politkovskaya have tarnished the image of Russian leaders, already criticized by the world community for their crackdown on democracy and free speech.