The widow of poisoned Russian emigre Alexander Litvinenko has asked British authorities to press ahead with an inquest that she hopes will shed light on suspected Russian state complicity in his murder.

Marina Litvinenko told Reuters she had decided on the move because there was no chance of Andrei Lugovoy, Britain's chief suspect, being extradited by Moscow to face trial in Britain for murdering her husband in London with radioactive polonium.

"Absolutely nobody will extradite him," she said in a telephone interview late on Monday.

Asked what she hoped to learn from an inquest, she said: "We just need the truth - what happened, and where this polonium came from."

She added: "We just need this justice ... I just need to feel one day we will receive this truth."

Russia has emphatically denied any role in the November 2006 murder of Litvinenko, a former KGB security official who had become an outspoken critic of the Kremlin and protege of exiled tycoon Boris Berezovsky, another thorn in Moscow's side. He died three weeks after the poison was slipped to him in a cup of tea.

Lugovoy has always protested his innocence.

Anglo-Russian relations plunged into crisis last year when Moscow refused a British request to hand over Lugovoy, another former KGB man. Each side expelled four of the other's diplomats in a Cold War-style tit-for-tat exchange.

An inquest, surrounded by huge publicity, would make it harder for the two sides to quietly draw a line under the affair and could hamper prospects for a thaw in relations under Russia's president-elect Dmitry Medvedev.

FORENSIC ANALYSIS

Alex Goldfarb, a friend of the Litvinenkos who heads a foundation which campaigns for justice for the family, said Marina's lawyer submitted the inquest request last Friday.

"She asks for a full inquest with discussion of the motive, the murder weapon and the possible complicity of the Russian government," he told Reuters.

Goldfarb says he believes British and U.S. authorities have already established the origin of the fatal polonium by isotopic

analysis, although they have not confirmed this publicly.

He said if it were proven that it was manufactured at a Russian state facility, this would increase pressure on Moscow to explain how it came into Lugovoy's hands.

"At the least, it would put an onus on the Russian government to explain itself," Goldfarb said.

Under British law, a dead person's family has the right to an inquest into a suspicious death. This often goes beyond the medical cause to examine more widely the circumstances of how the death occurred.

An inquest was opened and adjourned in 2006. Goldfarb said British Foreign Office and police officials had tried to discourage Marina from reopening it because they feared, respectively, that it would further damage relations with Moscow and reduce the already remote prospects for a trial.

A Foreign Office spokeswoman said: "We are in communication with Mrs Litvinenko but obviously we wouldn't be able to discuss any details of our communications with her." She said Britain was still seeking the extradition of Lugovoy.

Marina Litvinenko said she had met Foreign Secretary David Miliband last year, and spoken with police this month.

"I know for the police it is very important to get this case to court, but they can't do it without Lugovoy," she said. "I'm not sure I can wait 10 years for justice."