The murder of ex-Russian spy Alexander Litvinenko in 2006 in the UK was "probably" approved by President Vladimir Putin, a publicinquiry finds.
Mr Putin is likely to have signed off the poisoning of Mr Litvinenko with polonium-210 in part due to personal "antagonism" between the pair, it said.
Mr Litvinenko's widow Marina welcomed the report, calling for a travel ban on Mr Putin and sanctions on Russia.
The Russian Foreign Ministry said the inquiry had been "politicised".
It said: "We regret that the purely criminal case was politicised and overshadowed the general atmosphere of bilateral relations."
It said the inquiry had "not been transparent", saying it had not expected the process to be unbiased.
Mr Litvinenko died aged 43 in London in 2006, days after being poisoned with the radioactive substance. He was a former Russian spy but fled to Britain where he became a fierce critic of the Kremlin.
Gordon Corera, BBC security correspondent, said there were "audible gasps" inside the court when the conclusion of the report was revealed, adding it had been "stronger than expected".
Speaking outside London's High Court, Mrs Litvinenko said: "The words my husband spoke on his deathbed when he accused Mr Putin have been proved by an English court."
In a statement, Mrs Litvinenko urged the UK government to expel all Russian intelligence operatives and impose economic sanctions on Moscow.
She added that she still hoped for "final justice" for her husband's killers.
Home Secretary Theresa May is due to give the UK government's response to the findings in a statement to the House of Commons later.
Two Russian men, Andrei Lugovoi and Dmitry Kovtun, have been accused of Mr Litvinenko's murder. They both deny killing him.
Sir Robert said the two suspects were probably acting under the direction of Moscow's FSB intelligence service.
Singling out then-FSB chief Nikolai Patrushev, alongside Mr Putin, Sir Robert wrote in the 300 page report: "Taking full account of all the evidence and analysis available to me I find that the FSB operation to kill Litvinenko was probably approved by Mr Patrushev and also by President Putin."
Responding to the report, Mr Lugovoi, who is now a politician in Russia, said the accusations against him were "absurd", the Russian news agency Interfax was quoted as saying.
"As we expected, there were no surprises," he said.
"The results of the investigation made public today yet again confirm London's anti-Russian position, its blinkeredness and the unwillingness of the English to establish the true reason of Litvinenko's death."
Mr Kovtun, now a businessman in Russia, said he would not comment on the report until he got more information about its contents, Interfax reported.
London's Metropolitan Police said the investigation into the "cold and calculated murder" remained ongoing.