A former Russian spy poisoned in Britain and now hospitalized under guard may have been targeted for his criticism of former colleagues and his investigation into the killing of a prominent anti-Kremlin journalist, friends and fellow dissidents said Sunday.

Col. Alexander Litvinenko, a former KGB agent, said earlier this week that he fell ill on Nov. 1 following a meal with a contact who claimed to have details about the slaying of Anna Politkovskaya, the Russian journalist gunned down last month in Moscow.

Litvinenko was under armed guard at University College Hospital in London. The hospital said he was in "serious but stable" condition.

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"He is still very weak," friend Alexander Goldfarb told reporters outside the hospital. "He is in a fighting mood, though."'

A doctor treating Litvinenko told the British Broadcasting Corp. that tests showed he was the victim of poisoning by thallium — a toxic metal found in rat poison.

"He's got a prospect of recovering, he has a prospect of dying," said Dr. John Henry, a clinical toxicologist who treated Ukrainian President Viktor Yushchenko in 2004 after he was poisoned during his presidential election campaign. Henry said thallium can cause damage to the nervous system and organ failure, and that just one gram can be lethal.

In an interview with the Sunday Times before his condition worsened, Litvinenko described how he had lunch with an Italian contact who claimed to have had information on Politkovskaya's killing, which has not been solved.

British news outlets identified the contact as Mario Scaramella, an Italian academic who helped investigate KGB activity in Italy during the Cold War. Scaramella could not immediately be reached for comment.

"They probably thought I would be dead from heart failure by the third day," Litvinenko is quoted as saying in the Sunday Times. "I do feel very bad. I've never felt like this before — like my life is hanging on the ropes."

Police said a specialist crime unit began an investigation on Friday into how Litvinenko may have been poisoned. No arrests had been made so far, said a Scotland Yard spokesman, speaking on condition of anonymity in line with force policy.

Glenn Edwards, operations manager at Itsu restaurant where the lunch took place, told The Associated Press that detectives had arrived at the restaurant on Saturday asking for close circuit television footage.

Litvinenko left Russia for Britain six years ago and has become an outspoken critic of the Kremlin. In a 2003 book, "The FSB Blows Up Russia," he accused his country's secret service agency of staging apartment-house bombings in 1999 that killed more than 300 people in Russia and sparked the second war in Chechnya.

Boris Berezovsky, the Russian dissident and tycoon who was at Litvinenko's bedside on Friday, told The Associated Press he suspects Russia's intelligence services of the poisoning.

"It's not complicated to say who fights against him," Berezovsky said in a telephone interview. "He's [Russian President Vladimir] Putin's enemy, he started to criticize him and had lots of fears."

Goldfarb, who organized Litvinenko's emigration to Britain, said FSB agents had threatened him in the past.

"He looks like a ghost," Goldfarb said. "He's a very fit man, he never smoked, he never drank, he would run five miles a day, but now he has lost all his hair, he has inflammation in the throat, so he cannot swallow."

Russian authorities did not immediately comment on the allegations.

Litvinenko joined the KGB in 1988 and rose to the rank of colonel in its successor, the Federal Security Service, known as the FSB. He began specializing in terrorism and organized crime in 1991, and was transferred to the FSB's most secretive department on criminal organizations in 1997.

He fled Russia and claimed asylum in Britain in November 2000, two years after publicly accusing his FSB superiors of ordering him to kill Berezovsky, at the time a powerful Kremlin insider. Berezovsky said Sunday that Litvinenko fell out with his superiors after he exposed corruption within FSB ranks.

Before he left Russia, Litvinenko was jailed for nine months awaiting trial on charges of abusing his office; he was acquitted.

Kremlin critics claim poisoning — which is extremely hard to prove — is a common Soviet-era practice that seems to have reappeared since Putin, an ex-KGB officer, became president.

"It is not a secret that poisoning has become some kind of a trademark of a secret war in Russia," Alexander Golts, political commentator with the Russian news Web site Ezhenedelny Zhurnal, told the Associated Press. "I will not take the risk of accusing the government ... but certain groups have quite overtly been eliminating people they disliked through poisoning.

"It is absolutely obvious that this story with Litvinenko fits very well into the overall picture of power struggle in Russia," he said.

Politkovskaya, who had written critically about abuses by Russian forces fighting separatists in Chechnya, fell seriously ill after drinking tea on a flight from Moscow to southern Russia in 2004 during the school hostage crisis in Beslan. Colleagues say she was poisoned.

Yuri Shchekochikhin, a liberal Russian lawmaker and journalist who crusaded against corruption, died in July 2003 after apparently suffering a severe allergic reaction. Colleagues suspect he was poisoned, probably in connection with his reports on a case involving customs officials and allegations that a furniture store had evaded millions of dollars in import duties.

Yushchenko, the Ukrainian president, had his face badly disfigured by what doctors said was dioxin poisoning.

In one of the most notable Cold War assassinations, the Bulgarian dissident Georgi Markov was killed in 1978 with a poison dart concealed in an umbrella. British investigators long have suspected Bulgarian agents in the slaying.

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