LONDON — A former KGB colonel, Alexander Litvinenko, may have been poisoned with a radioactive substance previously used to try to kill a Soviet assassin who disobeyed orders.
Doctors in London said yesterday that the 43-year-old former spy's symptoms and the latest test results suggested the use of radioactive thallium.
The substance, used in tiny amounts to investigate cardiac blood flow problems, was used by the KGB in a failed attempt to kill Nikolai Khokhlov, an agent who refused to comply with an order to murder a prominent Russian dissident in 1957.
Mr. Litvinenko, who has lived in Britain for six years, was still in intensive care in a London hospital, although his condition has not worsened.
The Italian contact who met Mr. Litvinenko at a London sushi bar on the day he fell ill, Mario Scaramella, came out of hiding to disclose his version of events.
He said that at their meeting he told Mr. Litvinenko that he had received, from a confidential source, an alleged "hit list" that included both their names as well as that of an investigative journalist, Anna Politkovskaya, who was murdered last month.
Police are investigating suggestions that Mr. Litvinenko, a prominent Kremlin critic, could have had a drink or a meal spiked on November 1.
His friends have said he has information that would embarrass the Russian government. They have accused Russian agents of trying to assassinate him.
Senior government officials in Moscow have dismissed the claims as "sheer nonsense."
There have been allegations that Mr. Litvinenko has a tape that may be damaging to President Putin if it was made public. A clinical toxicologist at Imperial College London and a world expert on poisons, John Henry, spoke to Mr. Litvinenko at University College Hospital.
Mr. Henry said he no longer believed thallium sulphate to be the most likely poison used. "It is very likely that he has had radiation poisoning because his white cell count has gone down to zero. Now we are beginning to think it may well be radioactive thallium," he said.