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LONDON - Britain has put its crack anti-terrorism police unit on the case of a former Russian spy, who is fighting for his life after being poisoned in what his friends called a Kremlin assassination plot.
Russia dismissed as "pure nonsense" suggestions it had ordered the murder of former agent Alexander Litvinenko, 41, an outspoken critic of President Vladimir Putin.
Evidence of a Kremlin hand in such an incident on British soil would have far-reaching diplomatic consequences at a time of mounting concern in the West at Moscow's human rights record.
Litvinenko checked into a hospital at the beginning of the month after falling ill and was moved to another hospital when his condition worsened.
Toxicology reports now show he was poisoned by thallium, a chemical weapon that can cause a slow, painful death over the course of weeks or months, even with treatment.
Pictures released of him on Monday showed him strapped to medical equipment in hospital, wan and bald. Hair loss is one of thallium's effects.
The hospital said Litvinenko's condition had deteriorated slightly overnight and he had been transferred to intensive care. Doctors say he has only a 50/50 chance of surviving.
Police say they were called in to the case only last week -- two weeks after Litvinenko fell ill -- and are investigating whether he was deliberately poisoned.
They said in a statement that the counter-terrorism branch of London's Metropolitan police had taken over the case.
Officers were interviewing potential witnesses, including Litvinenko himself, studying his movements before he took sick and examining closed-circuit television pictures.
Alexander Goldfarb, who helped Litvinenko defect to Britain six years ago, told Reuters the former spy was the victim of a plot directed from the heart of the Russian government.
"This is a Kremlin-backed operation of Russian intelligence services -- whether it goes to the top of the Kremlin or to the top of the Russian secret service I cannot say," said Goldfarb, himself a Russian dissident who now has US citizenship.
In Moscow, deputy Kremlin spokesman Dmitry Peskov replied: "There is no need to comment on statements that are pure nonsense." An FSB spokesman declined comment and the Russian embassy in London described Litvinenko's case as an "accident".
Litvinenko has said he fell ill after meeting a source at a sushi restaurant while looking into the case of investigative journalist Anna Politkovskaya, a Putin critic gunned down at her Moscow apartment last month.
John Henry, a clinical toxicologist, told BBC radio there was no doubt he had been poisoned by thallium. "It is tasteless, colourless, odourless. It takes about a gram ... to kill you."
Litvinenko, now a British citizen, co-authored a book in 2002 entitled "Blowing up Russia: Terror from Within", in which he alleged FSB agents co-ordinated apartment block bombings in Russia that killed more than 300 people in 1999.
The bombings, which authorities blamed on Chechen rebels, led to a shift in public opinion in Russia, affording Putin popular backing for his decision to move troops into Chechnya.
Poison is an old tool of Cold War spycraft. In 1978, Georgi Markov, a Bulgarian dissident, was killed in London by a man who jabbed him with a poisoned umbrella.
But there are worries such Cold War-era killings could make a comeback. Ukraine's President Viktor Yushchenko fell ill after dining with security service leaders before an election in 2004. Doctors found he was poisoned with dioxin.
- REUTERS
