Nov. 24 (Bloomberg) -- Alexander Litvinenko, a former Russian spy poisoned in London while investigating the killing of an anti-Kremlin journalist, has died.

University College Hospital in London said in a statement last night that Litvinenko, 43, had died at 9:21 p.m. in intensive care.

Scotland Yard confirmed the ``unexplained death'' of Litvinenko. ``Inquiries continue into the circumstances surrounding how Mr Litvinenko became unwell,'' Scotland Yard said in an e-mailed statement.

Geoff Bellingan, director of critical care at University College Hospital, earlier yesterday said in a statement that Litvinenko's condition had suffered ``a dramatic deterioration'' and that he was ``critically ill.''

The former spy's sickness was not due to a heavy metal such as thallium, as previously thought, Bellingan said. It was also ``unlikely'' that he had suffered radiation poisoning, the doctor said. ``Despite extensive tests we are still unclear as to the cause of his condition,'' Bellingan said.

Litvinenko's family are ``all shocked and horrified at this terrible crime,'' the British Broadcasting Corp. cited family spokesman Alex Goldfarb as saying out side the hospital.

Litvinenko, 43, a former lieutenant colonel in Russia's FSB, or Federal Security Service, the successor to the KGB, claimed asylum in the U.K. six years ago and became an outspoken critic of the Kremlin over issues including the conflict in Chechnya.

Prominent Critic

He had been investigating the killing of Russian journalist Anna Politkovskaya, 48, another prominent critic of Russian President Vladimir Putin and his policy in Chechnya. Politkovskaya was shot at her Moscow apartment building Oct. 7.

Photographs of Litvinenko released Nov. 20 showed him looking frail in his hospital bed and that his hair had fallen out.

He first reported feeling ill on Nov. 1 after meeting with a friend at a Japanese sushi restaurant, Itsu, in London's Piccadilly.

Mario Scaramella, an Italian, said at a Nov. 21 news conference in Rome that he was the friend, the BBC reported. Scaramella said he and Litvinenko had both received e-mailed threats days before the poisoning, the BBC said.

To contact the reporters on this story: Nick Allen in London at nallen14@bloomberg.netScott Hamilton at shamilton8@bloomberg.net

Last Updated: November 23, 2006 20:49 EST