A "major dose" of radioactive material has been found in urine from former Russian spy Alexander Litvinenko, who died in a London hospital, British officials said Friday.

Former Russian security agent Alexander Litvinenko, in photo released by his family, died in London and in a statement blames the Kremlin.
(Family Handout/Associated Press)

Experts from the Radiation Protection Division of Britain's Health Protection Agency said Litvinenko had been exposed to alpha radiation likely from polonium-210, the most common isotope of the element polonium.

"This is an unprecedented event in the U.K. that someone has apparently been deliberately poisoned with a type of radiation," said Pat Troop. "We know he had a major dose."

To get that much radioactive material in the body, a person would have to have "eaten, inhaled or taken it in through a wound," she said.

Litvinenko died late Thursday in a London hospital from massive organ failure. In a statement dictated from his deathbed, he accused Russian President Vladimir Putin of poisoning him, a charge Putin denied.

The risk to people who had been in contact with Litvinenko, who spent days in two London hospitals, is low, officials said. Normal physical contact presents an extremely low risk, she said.

Experts are monitoring radiation levels at Barnet Hospital and University College Hospital, along with medical staff and family members who came in contact with Litvinenko, said Troop.

Scotland Yard confirmed late Friday traces of the element were found in Litvinenko's home in north London and at the Itso sushi bar near Piccadilly Circus where Litvinenko ate the day before he fell ill.

Low doses of the radioactive element could pose a small lifetime risk of cancer, said Prof. Roger Cox. Very high doses can harm bone marrow and cause organs to malfunction, he said.

Polonium-210 is a radioactive substance that can occur naturally in very low doses in food or the body. It can also be manufactured and has industrial uses.

Police search London

Earlier Friday, Britain's Home Office said police were searching London for radioactive material that could be linked to his death.

London's Metropolitan Police said it was treating the case as an "unexplained death," but not yet a murder.

Moscow has denied any involvement with the former spy, whose deathbed statement to Putin was read Friday in London by his friend Alex Goldfarb.

"You have shown yourself to have no respect for life, liberty or any civilized value. You have shown yourself to be unworthy of your office, to be unworthy of the trust of civilized men and women," Litvinenko's statement said.

"You may succeed in silencing one man, but the howl of protest from around the world, Mr. Putin, will reverberate in your ears for the rest of your life. May God forgive you for what you have done."

It's not clear when Litvinenko dictated the statement.

Putin on Friday extended his condolences but said he's seen no proof Litvinenko died a "violent death."

"This is not a violent death, so there is no ground for speculations of this kind," Putin said from a European Union summit in Helsinki, Finland.

Condition deteriorated rapidly

Litvinenko died at 9:21 p.m. local time Thursday at London's University College Hospital. A spokesperson for the hospital said New Scotland Yard would be investigating the death.

Friends said Litvinenko had been on a quest to uncover corruption in Russia's Federal Security Service, or FSB, and unmask the killers of another Putin critic, investigative journalist Anna Politkovskaya.

A fierce critic of the Russian government, Litvinenko had been under heavy sedation as doctors struggled to find the cause of his illness. His condition deteriorated rapidly on Thursday.

His friend, Andrei Nekrasov, told the Associated Press that before Litvinenko lost consciousness on Tuesday he said: "The bastards got me, but they won't get everybody."

Kremlin spokesman Dmitry Peskov on Monday called the poisoning allegations "sheer nonsense."

Dies surrounded by family

Litvinenko said he fell ill after eating a sushi dinner on Nov. 1 with a contact who reportedly had information connected to his investigation of Politkovskaya's murder. She was shot in her Moscow apartment building in October.

Walter Litvinenko, the father of the dead former Russian spy Alexander Litvinenko, reacts during a news conference outside University College Hospital in London on Friday.
(Matt Dunham/Associated Press)

His hair fell out, his throat became swollen and his immune and nervous systems were severely damaged.

Litvinenko's wife, father and one of his three children were with him when he died.

His father, Walter Litvinenko, who wept as he spoke outside the hospital, said his son was killed "by a little, tiny nuclear bomb.

"This regime is a murderous danger to the world … If we just let it go, if we go about our daily business as usual, this regime will get at all of us."

A former spy for the KGB and FSB, Litvinenko fled to Britain in 2000 after spending nine months in a Russian jail. He had been charged with abuse of office, but was later acquitted.

In 1998, Litvinenko went public with allegations he was ordered to kill Russian tycoon Boris Berezovsky, who is exiled in Britain.

Litvinenko recently received British citizenship.

With files from the Associated Press