LONDON, Nov 19: A former Russian spy and fierce critic of Russian President Vladimir Putin was fighting for his life in a London hospital on Sunday after an apparent bid to kill him by poisoning.

Alexander Litvinenko, a former lieutenant colonel in Russia's Federal Security Service (FSB) -- successor to the Soviet KGB -- fell ill after a Nov 1 meeting in a London sushi bar with a contact who purportedly had information on the murder of Russian journalist Anna Politkovskaya, said the Mail newspaper.

Specialist detectives launched an investigation as the 43-year-old lay in a University College Hospital bed in a serious but stable condition fighting what an expert said was poisoning by thallium, a toxic metallic element.

Friends of Litvinenko said they were in no doubt that the FSB was out to get the outspoken defector, who was granted political asylum in Britain in 2001.

A spokesman for London's Metropolitan Police told AFP: “Officers from the specialist crime directorate are investigating a suspicious poisoning.

“The inquiry is continuing and there's no arrest at this stage.”Litvinenko fled to Britain after blowing the whistle on an alleged FSB plot to assassinate Russian business oligarch Boris Berezovsky, who is also now living in Britain.

Litvinenko reportedly fell out with Putin when the president was head of the FSB in the late 1990s.—AFP