LONDON — President Vladimir Putin probably approved a plan by Russia’s FSB security service to kill former agent Alexander Litvinenko, who died three weeks after drinking tea laced with poison at a London hotel, a British judge said today.

In a lengthy report, Judge Robert Owen said that he is certain Litvinenko was given tea with a fatal dose of polonium-210, a radioactive isotope that is deadly if ingested even in tiny quantities, in November 2006.

He said there is a “strong probability” that the FSB, successor to the Soviet spy agency the KGB, directed the killing, and the operation was “probably approved” by Putin.

Before he died, Litvinenko accused Putin of ordering his killing, but this appears to be the first time anyone has officially linked Putin to it.

Moscow has always strongly denied involvement in Litvinenko’s death, and Russian Foreign Ministry spokeswoman Maria Zhakarova said Thursday that the government does not consider Owen’s conclusions to be objective or impartial.