Russia has dismissed the findings of a British inquiry into the poisoning death of former Russian spy, Alexander Litvinenko.
The report has concluded that Russian President Vladimir Putin 'probably' approved the murder ten years ago in London.
Russia's Foreign Ministry accuses Britain of wanting to vilify Russia and its officials.
On his deathbed, former Russian spy turned British agent Alexander Litvinenko accused Vladimir Putin of ordering his killing.
But this is the first public official statement linking the Russian president to the crime.
A British inquiry into the 2006 killing of Mr Litvinenko has concluded that two Russian men gave the ex-KGB agent tea containing a fatal dose of radioactive polonium-210 during a meeting at a London hotel.
Judge Robert Owen, who led the inquiry, has described the operation as "probably approved" by Mr Putin.
Russia has rejected the findings as politically motivated.
Russian Foreign Ministry spokeswoman Maria Zakharova says the report is neither objective nor impartial.
"There was only one aim and it was clear from the very beginning: to demonise Russia, demonise its official representatives and its leadership. This specific kind of investigation has not been transparent."
Mr Litvinenko's wife, Marina Litvinenko, welcomed the report and urged Britain to impose sanctions on Russia.
British Prime Minister David Cameron has responded to the finding that the Russian state is behind the poisoning of the outspoken critic of Vladimir Putin.
Mr Cameron says Britain has imposed an asset freeze on the two main Russian suspects and he has not ruled out further Russian sanctions.
"Well look, what happened was absolutely appalling and this report confirms what we've always believed which is it was state-sponsored action and that is why the last government took the action expelling Russian diplomats, issuing arrest warrants, refusing to cooperate with Russian intelligence agencies and those measures continue. What we've added today, rightly, is further asset freezes, writing again to the prosecuting authorities to see what more can be done."
Russia's ambassador to London has criticised Britain's handling of the death of Mr Litvinenko.
Alexander Yakovenko described the findings as a blatant provocation, adding that they will further harm relations between the two countries.
"The length of time that it took to close this case in this way makes us believe it to be a whitewash of the British Special Services incompetence. For us it's absolutely unacceptable that the report concludes that the Russian state was in any way involved in the death of Mr Litvinenko."
Russia has always refused to extradite suspects Andrei Lugovoi and Dmitry Kovtun, who claim they are innocent.
Mr Lugovoy has denied any involvement with the killing of Mr Litvinenko, calling the allegations a farce.
"Everything that is being said by British media referring to an open and public hearing, is a lie, an outrageous lie, and I can't find any other word to describe it."
The 43 year-old Alexander Litvinenko was a former spy who was regarded by Russia as having betrayed its security service, the FSB, by accusing it of bombing Russian apartment blocks in 1999 which the Kremlin blamed on dissident Chechens.
He was an outspoken critic of former FSB chief turned president Vladimir Putin and accused him and his administration of links to organised crime.
He died three weeks after drinking green tea laced with a rare and very potent radioactive isotope, polonium-210, at London's Millennium Hotel.
A friend of the Litvinenko family who gave evidence to the inquiry, Alexander Goldfarb, says the truth has finally been publicly confirmed.
"Well this report should tell you in the West what Sasha (Alexander) Litvinenko was trying to tell while he was alive: that you are dealing here with a murderous dictatorship, which is basically anti-Western and it took ten years to get his message through."