Russian prosecutors have officially rejected Britain's request for the extradition of a businessman accused in last year's fatal poisoning of former Russian spy Alexander Litvinenko.

Russian businessman Andrei Lugovoi speaks during a news conference in Moscow,  31 May 2007

The office of Russia's prosecutor general, in a statement, cited the ban in the country's constitution on the extradition of Russian citizens as the reason for its refusal to extradite Andrei Lugovoi.

But the statement expressed readiness to study the possibility of prosecuting the former KGB agent in Russia if Britain requests this and supplies sufficient evidence to justify it.

In May, Britain accused Lugovoi of involvement in the killing of Litvinenko, who died in November in London from a fatal dose of radioactive polonium- 210.

Russian authorities then opened their own investigation into Lugovoi's allegations that British secret services and a self-exiled billionaire, Boris Berezovsky, were responsible for Litvinenko's death.

Lugovoi, who met with Litvinenko in London last November, on the day the former spy fell ill, maintains his innocence in the death.

On his deathbed, Litvinenko accused Russian President Vladimir Putin of ordering his poisoning - a charge the Kremlin denies.

Some information for this report was provided by AFP and AP.