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In Britain, a former Russian spy turned critic of President Vladimir Putin has been moved to the intensive care unit of a London hospital. Alexander Litvinenko was poisoned earlier this month. His condition worsened overnight.

As NPR's Rob Gifford reports from London, a senior Kremlin spokesman has dismissed allegations that the Russian government was involved in his poisoning.

ROB GIFFORD: Alexander Litvinenko is a former colonel in the Russian Federal Security Service, the successor to the KGB. Now he is an outspoken critic of the Kremlin and had been looking into the killing of Russian investigative journalist Anna Politkovskaya, also a fierce critic of Russian president Vladimir Putin.

Last week, Litvinenko told the BBC that on November 1, a former KGB man he knew from Moscow suggested meeting for a drink in London.

Mr. ALEXANDER LITVINENKO: (Through Translator) Someone came up to me and said that we should meet. The meeting took place in a restaurant in London. He gave me some papers which contained some names, perhaps names of those who may have been involved in the murder of Anna Politkovskaya. And several hours after the meeting, I started to feel sick.

GIFFORD: Alexander Goldfarb is a friend of Litvinenko's who helped him defect to Britain six years ago. He visited him yesterday in the hospital.

Mr. ALEXANDER GOLDFARB: He looks like a ghost or like a cancer patient who went through a heavy chemotherapy. He lost all his hair, is very thin. He absolutely hasn't eaten for 19 days now, and they feed him through IV. And what is more important they say that his bone marrow is gone. He doesn't produce white cells. So he's very susceptible to infection.

GIFFORD: In 2004, Ukrainian President Victor Yushchenko nearly died after being poisoned. Alexander Litvinenko was one of those who accused Moscow at the time of being behind that incident. The toxicologist who treated the Ukrainian president is now also treating dissident Litvinenko in London.

Dr. John Henry said there is no doubt Alexander Litvinenko has been poisoned with the chemical thallium.

Dr. JOHN HENRY: Thallium is a chemical that comes in salts. A little bit like table salt. It is tasteless, colorless, odorless. It takes about, you know, a large pinch salt in your food to kill you.

GIFFORD: Kremlin spokesmen said today that any suggestion that the Russian government had been involved in the poisoning was nothing but sheer nonsense. But another former KGB defector in London, Oleg Golievski, said many people know exactly who poisoned Litvinenko.

Mr. OLEG GOLIEVSKI: The name was (unintelligible) actually to many people. Not to the wife of Mr. Litvinenko, Marena. But unfortunately he will be hiding in Moscow. But then he will never been able to come to Britain and any European country again because he will on the black list.

GIFFORD: London has long been a center of espionage and intrigue. In 1978, Bulgarian dissident Georgi Markov was killed with a poison tipped umbrella containing the poison ricin on Waterloo Bridge. Alexander Litvinenko is fighting for his life under armed guard in a London hospital. Doctors have given him a 50/50 chance of survival.

Rob Gifford, NPR News, London. Transcript provided by NPR, Copyright NPR.