Jill Lawless / AP - A former KGB agent turned Kremlin critic who blamed a "barbaric and ruthless" Russian President Vladimir Putin for his fatal poisoning had a toxic radioactive substance in his body, the British government said Friday.

In the statement dictated from his deathbed, Alexander Litvinenko accused the Russian leader of having "no respect for life, liberty or any civilized value." In his first public response to the allegations, Putin said he deplored the former spy's death but called the statement a political provocation.

The Health Protection Agency said the radioactive element polonium-210 had been found in Litvinenko's urine.

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

"We know he had a major dose," she said.

Earlier, Home Secretary John Reid said Litvinenko's death Thursday night was "linked to the presence of a radioactive substance in his body."

Litvinenko, a vociferous critic of the Russian government, suffered heart failure late Thursday after days in intensive care at London's University College Hospital battling a poison that had attacked his bone marrow and destroyed his immune system.

"You may succeed in silencing me but that silence comes at a price. You have shown yourself to be as barbaric and ruthless as your most hostile critics have claimed," Litvinenko said in the statement read by his friend and spokesman Alex Goldfarb. The former spy said "the howl of protest from around the world will reverberate, Mr. Putin, in your ears for the rest of your life."

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

Litvinenko's father Walter said his son "fought this regime and this regime got him."

"It was an excruciating death and he was taking it as a real man," Walter Litvinenko said.

Putin's government strongly denied involvement.

"A death of a man is always a tragedy and I deplore this," Putin said after being asked about Litvinenko during a news conference after summit talks 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 provocations," he said.

Litvinenko told police that he believed he had been poisoned on Nov. 1, while investigating the slaying of crusading journalist Anna Politkovskaya. His hair fell out, his throat became swollen and his immune and nervous systems were severely damaged.

He was transferred from a north London hospital to University College Hospital on Nov. 17 when his condition deteriorated.

Doctors treating him acknowledged they could not explain his rapid decline. They discounted earlier theories that the 43-year-old father of three had been poisoned with the toxic metal thallium and cast doubt on an alternative diagnosis of a radioactive substance.

The hospital said Friday it could not comment further because the case was being investigated by police. London's Metropolitan Police said it was treating the case as an "unexplained death" _ but not, yet, a murder.

Litvinenko's friends had little doubt about who was to blame.

They said Litvinenko, who sought asylum in Britain in 2000, had been on a quest to uncover corruption in Russia's Federal Security Service, or FSB, and unmask the killers of Politkovskaya, another trenchant critic of Putin's government.

Goldfarb said the attack on Litvinenko bore "all the hallmarks of a very professional, sophisticated and specialist operation."

"The very fact that experts are still at a loss to say what poisoned him tells you it is not a sleeping pill that has been given to him," he said.

Another friend, Andrei Nekrasov, said Litvinenko had told him: "The bastards got me, but they won't get everybody."

He said Litvinenko believed he had been targeted by the Kremlin because he had threatened to uncover embarrassing facts.

"The only logic is revenge, they consider him an enemy _ every week he was in Putin's face, he was a tireless critic of Putin's regime ... He had a mission to uncover what he felt were crimes his former colleagues had committed," Nekrasov said.

Litvinenko worked for the KGB and its successor, the FSB. In 1998, he publicly accused his superiors of ordering him to kill tycoon Boris Berezovsky and spent nine months in jail from 1999 on charges of abuse of office. He was later acquitted and in 2000 sought asylum in Britain, where Berezovsky is now also living in exile.

On the day he first felt ill, Litvinenko said he had two meetings, the first with an unnamed Russian and Andrei Lugovoy, an-KGB colleague and bodyguard to former Russian Prime Minster Yegor Gaidar.

Later, he dined with Italian security expert Mario Scaramella to discuss the October murder of Politkovskaya.

Scaramella said he showed Litvinenko an e-mail he received from a source naming Politkovskaya's killers, and naming other targets including Litvinenko and himself.

Russischer Ex-Agent Litwinenko in London gestorben