Russian President Vladimir Putin "probably" approved the killing of Russian exile Alexander Litvinenko, an inquiry in Britain has found.
Following a 12-month investigation the chairman of the government inquiry, Robert Owen, said he had concluded that former Russian military officer Dmitry Kovtun and a Russian associate, Andrei Lugovoi, poisoned Litvinenko in 2006 under direction from the FSB, Russia's state security agency.
"I am sure that Mr Lugovoi and Mr Kovtun were acting under the direction of others when they poisoned Mr Litvinenko," Owen said in his report, adding that both suspects were likely to have been directed by the FSB.
"The FSB operation to kill Mr Litvinenko was probably approved by Mr Patrushev and also by President Putin," he said, referring to Nikolai Patrushev, who was head of the FSB in 2006.
Litvinenko, an exiled former Russian spy turned British informant, fled to Britain in 2000 and became an outspoken critic of Putin.
He is believed to have ingested polonium-210, which is produced in nuclear reactors, at a meeting in London with Kovtun and Lugovoi.
Litvinenko's widow, Marina Litvinenko, welcomed Thursday's findings and urged Prime Minister David Cameron to expel all Russian intelligence officers from Britain and impose "targeted economic sanctions" and travel bans on Russians linked to her husband's death, including Patrushev and Putin.
She said she had received a letter from Home Secretary Theresa May on Wednesday, "promising action."
British prosecutors had accused Kovtun and Lugovoi of involvement in Litvinenko's murder, but the Russian government refused to extradite them to answer the charges.
On Thursday, Russian officials again said they would not extradite the two suspects and claimed the British inquiry was politically motivated.
"We regret that the purely criminal case has been politicized and has marred the entire atmosphere of bilateral relations," Russia's Tass news agency quoted foreign ministry spokeswoman Maria Zakharova as saying.
Zakharova said Britain's decision to suspend an earlier coroner's inquest and open a public inquiry into Litvinenko's death was "clearly politically motivated."
Moscow planned to present a "detailed review" of the inquiry report after analysing it, the Interfax news agency said.
Lugovoi said the allegations against him were "nonsense," Interfax said.