London: A British security services agent says the Russian government may have been involved in the 2006 murder of former security agent and Kremlin critic Alexander Litvinenko in London, according to the BBC's Newsnight programme aired on Monday night.

The unnamed security officer told Newsnight there were strong indications the government of former president Vladimir Putin was involved in Litvinenko's murder, according to the report. Putin is now Russia's prime minister.

In the Newsnight report, the agent's voice is heard speaking but no face is seen. "We very strongly believe the Litvinenko case to have had some state involvement," the officer is heard saying during the half-hour programme featuring news analysis on several subjects.

Separately, a British security official, speaking on condition of anonymity, said some Russian state involvement in the killing could not be entirely ruled out.

Officials at the Kremlin were not immediately available to comment on the report.

Litvinenko, a renegade officer of Russia's Federal Security Service, or FSB - the successor agency to the KGB - had been living in asylum in Britain when he died in a London hospital after ingesting radioactive polonium-210.

Deathbed statement

In a deathbed statement, he accused Putin of being behind his killing - charges the Kremlin has fiercely denied.

The BBC programme also said that officials from MI5 had said they believed they had stopped Russian security services from killing another Kremlin critic, Boris Berezovsky, in London last year. Newsnight said a Russian citizen was arrested and deported in June 2007 in connection with the alleged incident. Berezovsky told Newsnight that British authorities had not put the man on trial because they did not want to reveal their sources, according to the report.

The security official declined to comment on Berezovsky's claim.

Berezovsky has been an outspoken critic of Putin and is wanted in Russia on embezzlement and other charges - all of which he denies. Litvinenko's murder has strained diplomatic relations between Russia and Britain. Jonathan Evans, head of Britain's security service MI5 said recently he believes Russian spies are operating in Britain under diplomatic cover.