Alexander Litvinenko, 43, a former officer of the Federal Security Service (FSB) and allegedly a close associate of Russia's fugitive oligarch Boris Berezovsky, is now in a London hospital with symptoms of severe poisoning.
"There has been a major deterioration in Mr. Litvinenko's condition overnight," the hospital said in a statement. "He is now in a very serious condition and remains in intensive care."
Litvinenko was admitted to a London hospital two weeks ago and diagnosed with acute poisoning initially believed to have been caused by a potentially deadly concentration in his blood of thallium, a chemical used in rat poison and insecticides.
"Mr. Litvinenko is being treated and monitored in the intensive care unit of University College Hospital so he can receive cardiac monitoring and specialist support in areas such as nutrition and pain relief," the statement said. "He can also be more effectively isolated to protect him against infection, following the damage to his immune system."
The alleged poisoning is being investigated by Britain's Scotland Yard, while Russia's foreign intelligence service has already denied any involvement in the case.
The former secret agent fled Russia after three criminal cases were opened against him in 2000. He was later granted political asylum by the British government.
