Almost a decade after former KGB officer Alexander Litvinenko lay dying in a London hospital bed, a British judge has concluded who poisoned him: two Russian men, acting at the behest of Russia's security services, probably with approval from President Vladimir Putin.

That finding prompted sharp exchanges Thursday between London and Moscow, and a diplomatic dilemma for both countries. With Russia and the West inching closer together after years of strain, neither side wants a new feud — even over a state-sanctioned murder on British soil.

Judge Robert Owen, who led the public inquiry into the killing, said he was certain that two Russians with links to the security services had given Litvinenko green tea containing a fatal dose of radioactive polonium-210 during a meeting at a London hotel. He said there was a "strong probability" that Russia's FSB, the successor to the Soviet Union's KGB spy agency, directed the killing and that the operation was "probably approved" by Putin, then as now the president of Russia.

Before he died, Litvinenko accused Putin of ordering his killing, but Owen's report is the first public official statement linking the Russian president to the crime, and it sent a chilling jolt through U.K.-Russia relations.

British Prime Minister David Cameron said the evidence in the report of "state-sponsored" killing was "absolutely appalling." Britain summoned the Russian ambassador for a dressing-down and imposed an asset freeze on the two main suspects: Andrei Lugovoi, now a Russian lawmaker, and Dmitry Kovtun.

Home Secretary Theresa May said the involvement of the Russian state was "a blatant and unacceptable breach of the most fundamental tenets of international law and of civilized behavior."

Moscow has always strongly denied being involved in Litvinenko's death and accused Britain of conducting a secretive and politically motivated inquiry.

Putin spokesman Dmitry Peskov told reporters that the "quasi-investigation" would "further poison the atmosphere of our bilateral relations."

He said the report "cannot be accepted by us as a verdict."

Russian Foreign Ministry spokeswoman Maria Zhakarova said the British inquiry was neither public nor transparent, saying it had turned into a "shadow puppet theater."

"There was one goal from the beginning: slander Russia and slander its officials," she told reporters in Moscow.

Litvinenko fled to Britain in 2000 and became a critic of Russia's security services and of Putin, whom he accused of links to organized crime and other alleged transgressions including pedophilia, Owen said in the report. He was a very vocal annoyance, feeding inside information about Russia's secrets to Western intelligence services, and — the judge said — was widely regarded within the FSB as a traitor.

"There were powerful motives for organizations and individuals within the Russian state to take action against Mr. Litvinenko, including killing him," Owen wrote in the 326-page report.

The judge said the case for Russian state involvement was circumstantial but strong. Owen said Litvinenko had "personally targeted President Putin himself with highly personal public criticism," allied himself with Putin's opponents and was believed to be working for British intelligence.

Litvinenko had co-written a book in which he blamed former FSB superiors of carrying out bombings of Russian apartment buildings in 1999 that were blamed on Chechen militants. He also accused Putin of being behind the 2006 contract-style slaying of Anna Politkovskaya, a journalist who exposed human rights abuses in Chechnya.

Owen said the method of killing, with radioactive poison, fit with the deaths of several other opponents of Putin and his government, and noted that Putin had "supported and protected" Lugovoi since the killing, even awarding him a medal for service to the nation.

"I am sure that Mr. Lugovoi and Mr. Kovtun placed the polonium-210 in the teapot at the Pine Bar on 1 November 2006," he wrote — probably under the direction of the FSB.

He said the operation to kill Litvinenko was "probably" approved by then-FSB head Nikolai Patrushev, now head of Putin's security council. He said it was "likely" the FSB chief would have sought Putin's approval for an operation to kill Litvinenko.

Marina Litvinenko, the spy's widow, said she was "very pleased that the words my husband spoke on his deathbed when he accused Mr. Putin have been proved by an English court."

She urged Cameron to expel Russian intelligence agents operating in Britain and impose economic sanctions and travel bans on Putin and other officials linked to what her lawyer, Ben Emmerson, called "a mini-act of nuclear terrorism on the streets of London."

"It's unthinkable that the prime minister would do nothing in the face of the damning findings," Marina Litvinenko told reporters.

Britain's scope for strong action is limited, however.

U.K.-Russian relations have remained chilly since the killing of Litvinenko, who was granted British citizenship shortly before his death, and worsened with Russia's involvement in the separatist fighting in Ukraine. But the inquiry's report comes as the two countries are cautiously trying to work together against the Islamic State group in Syria, and neither wants a major new rift.

May, the home secretary, announced asset freezes against Lugovoi and Kovtun, and said Interpol had issued notices calling for their arrest if they traveled abroad. Russia refuses to extradite them.

Lugovoi is now a member of the Russian parliament, which means he is immune from prosecution in his country. In an interview with The Associated Press, he called the British investigation a "spectacle."

"I think that — yet again — Great Britain has shown that anything that involves their political interests, they'll make a top priority," he said.

Lugovoi also claimed he would have liked to testify at the inquiry but "was not allowed." The judge said both Lugovoi and Kovtun declined to give evidence.

Kovtun, now described as a businessman, told the Tass news agency that the conclusions were based on "false evidence" presented in closed hearings.

Political figures in Russia have cast the political inquiry as politically driven by a hostile West, and have highlighted the fact that parts were held in private because Britain was unwilling to disclose intelligence material.

Vyacheslav Nikonov, a political analyst close to the Kremlin, called the case "a black box into which no one was allowed to look, except for the judge," and claimed "decisions were made for purely political reasons."

Dmitry Oreshkin, an opposition-minded Russian political analyst, said the findings meant "the relationship with the West will systematically get worse" — something that suited Putin's interests.

Owen, a retired High Court judge appointed by the government to head the inquiry, heard from dozens of witnesses during months of public hearings last year and also saw secret British intelligence evidence.

In his report, the judge laid out the overwhelming scientific evidence against Lugovoi and Kovtun, including a trail of radiation that stretched from the hotel teapot to the sink in Kovtun's room and even to Emirates Stadium, the home of the Arsenal soccer team where Lugovoi attended a game.

Litvinenko died after three agonizing weeks in which his hair fell out, he vomited blood and his organs failed. A urine test conducted by a doctor on a hunch shortly before Litvinenko's death revealed the presence of polonium-210, an isotope that is deadly if ingested in tiny quantities.

He lapsed into unconsciousness Nov. 22, after telling his wife he loved her and died of heart failure the next day. His body was so radioactive that he was buried in a lead-lined coffin in London's Highgate Cemetery.


Associated Press writers Katherine Jacobsen, Lynn Berry and Vitnija Saldava in Moscow and Sylvia Hui in London contributed.