London: Russian President Vladimir Putin "probably approved" the killing of former KGB agent Alexander Litvinenko who died in a hospital here in 2006 from radioactive poisoning, a British inquiry concluded on Thursday in a damning report, triggering a diplomatic row with Moscow.
43-year-old Litvinenko, a former agent in the Russian federal security service (FSB) or secret police, died days after being poisoned with radioactive polonium-210 which he is believed to have drunk in a cup of tea.
The finding by Robert Owen, a retired High Court judge, in a 328-page report represented by far the most damning official link between Litvinenko's death and the highest levels of the Kremlin.
While he lay dying in a London hospital bed, Litvinenko had pointedly told Scotland Yard that the Russian President had given the orders for his killing.
There is a "strong probability" they were acting on behalf of the Russian FSB secret service, the inquiry found.
Two Russian men, Andrei Lugovoi and Dmitry Kovtun, have been accused of his murder. They deny killing him.
Owen said that taken as a whole the open evidence that had been heard in court amounted to a "strong circumstantial case" that the Russian state was behind the assassination.
But when he took into account all the evidence available to him, including a "considerable quantity" of secret intelligence that was not aired in open court, he found "that the FSB operation to kill Litvinenko was probably approved by [Nikolai] Patrushev [head of the security service in 2006] and also by President Putin".
At the time of his death, Litvinenko was working for the British intelligence service MI6 and also for Spanish intelligence, passing on information on Russian organised crime networks and their links to the Kremlin. Litvinenko was due shortly to become a star witness in a number of trials.
British Prime Minister David Cameron's official spokeswoman said Downing Street was taking the findings "extremely seriously" and that the Prime Minister found them "extremely disturbing".
The spokeswoman said: "The conclusion that the murder was authorised at the highest levels of the Russian state is extremely disturbing. It is not the way for any state, let alone a permanent member of the UN Security Council, to behave.
"Regrettably, these findings confirm what we and previous governments already believed."
The spokeswoman said measures taken against Russia in 2007 remained in place, adding: "In the light of the inquiry's findings, we are considering what further action we should take."
In Moscow, Russian Foreign Ministry spokeswoman Maria Zakharova said, "We regret that a purely criminal case was politicised and darkened the general atmosphere of bilateral relations.