"You may succeed in silencing one man but the howl of protest from around the world will reverberate, Mr. Putin, in your ears for the rest of your life."

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Goldfarb said Litvinenko dictated the statement before he lost consciousness Tuesday, and signed it in the presence of his wife, Marina.

Putin strongly denied involvement by his government.

"A death of a man is always a tragedy and I deplore this," the Russian leader said when asked about Litvinenko during a news conference after a meeting with European Union leaders.

Putin said the fact that Litvinenko's statement was released only after his death showed it was a provocation. "It's extremely regrettable that such a tragic event as death is being used for political provocation," he said.

At a meeting Friday with Russian Ambassador Yury Fedotov at London's Foreign Office, British diplomats asked Moscow to provide all assistance necessary to a police inquiry into the death, government officials said. Putin pledged to cooperate.

Home Secretary John Reid convened the British government's crisis committee Friday to discuss the death, a Cabinet Office spokeswoman said. Prime Minister Tony Blair's Downing Street office said he was in Scotland and did not attend.

In Washington, State Department spokesman Tom Casey said the United States has sought information on the case from British authorities. "We have been told that they have no definitive conclusions and that they are conducting an investigation," Casey said.

The Health Protection Agency described poisoning with polonium-210 as "an unprecedented event."

"I've been in radiation sciences for 30-odd years and I'm not aware of any such incident," said Roger Cox, director of the agency's center for radiation, chemicals and environmental hazards.

The agency's chief executive, Pat Troop, said the high level of polonium-210 indicated Litvinenko "would either have to have eaten it, inhaled it or taken it in through a wound."

Troop said the agency was evaluating whether it was safe to perform an autopsy.

Peter Clarke, head of London's anti-terrorist police, said officers and military radiation experts were searching several locations in London. A police statement later said at least five locations were being checked, but did not identify two of them.

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