LONDON -- A British judge says President Vladimir Putin probably approved a plan by Russia's FSB security service to kill former agent Alexander Litvinenko.

Judge Robert Owen said Thursday in a lengthy report that he is certain Litvinenko was given tea laced with a fatal dose of polonium-210 at a London hotel in November 2006.

He said there is a "strong probability" that the FSB directed the killing, and the operation was "probably approved" by Putin.

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Litvinenko, who had become a vocal critic of Russian President Vladimir Putin, died after ingesting the polonium-210, an isotope that is deadly if ingested in tiny quantities.

He had fled from Russian to Britain in 2000 after breaking with Putin and his inner circle. In 2006, he met two Russian comrades -- Dmitry Kovtun and Andrei Lugovoi -- for tea at London's upmarket Millenium Hotel.

CBS News correspondent Charlie D'Agata reports Litvinenko became violently ill and was dead within three weeks. A urine test confirmed the polonium-210 poisoning.

On his death bed, Litvinenko told his wife, "Putin did it."

Today, Maria Litvinenko told reporters in London she was glad her husband's claim had "been proved."

British police have accused Kovtun and Lugovoi of slipping the poison into Litvinenko's pot of tea, carrying out the killing sponsored by elements in the Kremlin. Both deny involvement, and Moscow refuses to extradite them.

The British government announced in the wake of the report Thursday that it was freezing assets belonging to Lugovoi and Kovtun.

Home Secretary Theresa May, who is in charge of justice issues, also told British lawmakers the government was summoning the Russian ambassador to the Foreign Office to express its "profound displeasure."

May called the report's conclusion "deeply disturbing," and described Russia's alleged actions as a "blatant and unacceptable breach of international law and civilized behavior."

Lugovoi, a Russian lawmaker, dismissed the report Thursday as "absurd."

"The accusations against me are absurd," Lugovoi said, according to the Russian news agency Interfax. "The results of the inquiry made public today once again confirm London's anti-Russian stance, tunnel thinking and the unwillingness of the British to establish the true cause of Litvinenko's death."

The case led to a souring of British ties to Russia.