A former Russian spy fighting for his life in a London hospital was poisoned at the behest of the Kremlin after years of stinging criticism against the Moscow regime, prominent Russian exiles alleged Monday.

Russian authorities denied any link to the man's condition. Police counterterrorism officials took charge of the investigation.

Col. Alexander Litvinenko, a former KGB and Federal Security Bureau agent, was under armed guard at a London hospital, as authorities investigated a case that has all the hallmarks of a Cold War thriller.

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Doctors said Litvinenko was seriously ill after being given the deadly poison thallium — a toxic metal found in some types of rat poison that can cause damage to the nervous system and organ failure. Such poison has been outlawed in Britain since the 1970s, making it highly unlikely any could have gotten into his food by accident.

Photographs released by the hospital showed a wan man in a green hospital gown, his bald head propped up by pillows, his arm hooked to an IV drip. Thallium causes hair loss and interferes with the cardiovascular and nervous systems, attacking the vital organs.

Litvinenko's condition deteriorated Monday, and he was moved to intensive care. His white cell count is down to nearly zero, said Dr. John Henry, a clinical toxicologist involved in his care.

"It shows his bone marrow has been attacked and that he is susceptible to infection," Henry said.

Litvinenko, who has been a thorn in the Russian government's side since the late 1990s, fell ill after a meal with a contact who claimed to have details about the slaying of another Kremlin critic — Russian investigative journalist Anna Politkovskaya, who was gunned down Oct. 7 inside her Moscow apartment building.

Litvinenko publicly blamed the killing on Russian President Vladimir Putin.

"Somebody has asked me directly, who is guilty of Anna's death? And I can directly answer you: it is Mr. Putin, president of the Russian Federation," he told a videotaped meeting discussing Politkovskaya's death at a media club in London in October.

Other Russian dissidents in Britain also blamed the Kremlin.

"Permission to assassinate abroad can only be given from the top," Oleg Gordievsky, former deputy head of the KGB at the Soviet Embassy in London told The Associated Press. "How can it not be state-sponsored?"

"He was for five years attacking Putin and the head of the [secret services] week in, week out. He was deliberately irritating the whole of the Russian establishment, particularly Putin."

In Moscow, Kremlin spokesman Dmitry Peskov dismissed suggestions that Russian intelligence services were involved as "nothing but sheer nonsense."

But exiled Russian dissident Boris Berezovsky was adamant that Putin, a former spy himself, was not only aware of the operation, but gave the orders.

"There's no doubt Putin gave the command to kill him," said the multimillionaire, who claimed that Litvinenko had also been targeted a year ago, when a grenade was thrown into his home.

In a statement, police said they were awaiting the results of toxicology tests, and did not want to speculate on what had caused Litvinenko's condition. They said they were interviewing witnesses and reviewing security video footage. No arrests have been made.

Alexander Goldfarb, who helped Litvinenko seek asylum in Britain in 2000, said the poison might have been sprinkled into Litvinenko's drink during a meeting at a central London hotel on Nov. 1 before he went to meet the contact at a sushi restaurant.

Litvinenko briefly met two men from Moscow — one a former KGB officer he knew — for tea at the hotel, Goldfarb said.

"I called Alexander in hospital ... he told me it is true, on that day, before meeting the Italian, he met with two Russians," Goldfarb said, adding that Litvinenko had not previously met the second man.

Litvinenko told police about the two men, he said.

In Rome, Mario Scaramella, a security expert identified in media reports as the man Litvinenko met at the restaurant, declined to comment about the meeting. But Paolo Guzzanti, an Italian senator and former head of parliamentary commission that examined cases of past KGB infiltration, said he has been in daily contact with Scaramella and confirmed he had met with the former spy on Nov. 1.

After hearing of Litvinenko's poisoning, "Scaramella went to the British Embassy in Rome and made himself available, but nobody questioned him," Guzzanti said. The British Embassy in Rome declined to comment.

Litvinenko joined the KGB counterintelligence forces in 1988, and rose to the rank of colonel in 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.

Litvinenko quit Russia for Britain six years ago and has been an outspoken critic of the Kremlin ever since.

In 2003 he wrote a book, "The FSB Blows Up Russia," accusing 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.

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