The finding by Robert Owen, a retired High Court judge, in a 328-page report, represented by far the most damning official link between Mr. Litvinenko’s death on Nov. 23, 2006, and the highest levels of the Kremlin.

The report could revive strains in relations between Britain and Russia, which were plunged into a chill reminiscent of the Cold War by the death of Mr. Litvinenko, a whistle-blower who had fought corruption in Moscow’s security services.

Speaking after the release of the report, Mr. Litvinenko’s wife, Marina, 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.”…

“Taking full account of all the evidence and analysis available to me,” Judge Owen said in the report, “I find that the F.S.B. operation to kill Mr. Litvinenko was probably approved by Mr. Patrushev and also by President Putin.”