The man suspected of poisoning ex-KGB agent Alexander Litvinenko has said it could not have happened without the involvement of British secret services.
Andrei Lugovoi, who denies killing Mr Litvinenko, told a Moscow news conference that he was a scapegoat.
Mr Lugovoi said MI6 had recruited Mr Litvinenko and had also tried to recruit him, to collect information on Russian President Vladimir Putin.
The UK said the matter was a criminal rather than an intelligence matter.
"A British citizen was killed in London and UK citizens and visitors were put at risk," a Foreign Office spokesman said.
KEY EVENTS IN CASE
1 November 2006: Alexander Litvinenko meets Andrei Lugovoi and another Russian at a London hotel
23 November 2006: Litvinenko dies in a London hospital
24 November 2006: A Litvinenko statement accuses Russian President Vladimir Putin of involvement in his death. Experts say Litvinenko was poisoned
6 December 2006: UK police say they are treating the death as murder
22 May 2007: Lugovoi should be charged with Litvinenko's murder, British prosecutors say
28 May 2007: UK makes formal request for Lugovoi's extradition from Russia
The UK has requested Mr Lugovoi's extradition in connection with the crime. But the Russian constitution forbids it from extraditing its own citizens.
Mr Litvinenko died in November 2006 after exposure to the radioactive isotope polonium-210.
Polonium-210 was found in a string of places that Mr Lugovoi visited in London, but he said he was a witness, not a suspect in the case.
A former KGB officer and British agent, Oleg Gordievsky, described Mr Lugovoi's claims as "silly fantasies". He denied Mr Litvinenko had been working for the British secret services.
"He used to be... a member of the FSB, it is a domestic organisation of the KGB, and MI6 is not interested in information about the domestic service, so Litvinenko was not needed," he told BBC News.
Mr Lugovoi, himself an ex-KGB agent, said the poisoning could not have happened without some involvement from the British intelligence services.
"Even if [British special services] hadn't done it itself, it was done under its control or connivance," he said.
Asked if he had evidence of this, Mr Lugovoi said he did, without giving further details.
Mr Lugovoi said that either British foreign intelligence agency MI6, the Russian mafia, or fugitive Kremlin opponent Boris Berezovsky were behind the killing.
Mr Lugovoi said that, like Mr Litvinenko, Mr Berezovsky was working for the British secret services, but that the two men had a falling out and that MI6 could no longer control Mr Litvinenko.
Mr Berezovsky, who has been granted asylum in Britain, has denied any involvement in Mr Litvinenko's death.
On Thursday, Mr Berezovsky said that it was now "clearer than ever" that the Kremlin was behind the murder.
"Everything about Mr Lugovoi's words and presentation made it obvious that he is acting on Kremlin instruction. If Mr Lugovoi would like to prove his innocence, I suggest again that he travel to London and face trial in the UK courts," he said in a statement.
Mr Lugovoi said he was "openly recruited as the British security service agent. They asked me to collect any... compromising information about President Putin and the members of his family".
He said he was initially asked to find economic information, but he said the large fees he was paid made him realise he was being recruited to do more than that.
He went on to say that he lacked the motive to kill Mr Litvinenko.
"Sasha [Litvinenko] was not my enemy. I didn't feel cold or hot from whatever he was doing, from the books that he was writing. I've been in business for a long time and I was not really interested," he said.
Mr Lugovoi also spoke about Russians who managed to get British passports by working for special services. The British public, he said, should know what certain Russians were doing in London.