MOSCOW - Russian authorities hope to receive permission as early as this week to send investigators to Britain to probe the poisoning death of former security agent Alexander Litvinenko, the chief prosecutor's office said Sunday.

Andrei Lugovoi, a businessmen who was formerly in the Russian security services and reported by British media to be a suspect in the radiation poisoning murder of former security agent Alexander Litvinenko, fires a pistol at a shooting gallery somewhere in undisclosed location in Russia, in this undated image from the television broadcast, Sunday, Feb. 4, 2007. [AP]

Russian prosecutors have asked to send a team to Britain to make inquiries in the poisoning case, which has damaged the image of Russian President Vladimir Putin and his government.

The Prosecutor General's Office has received no official response but hopes for approval soon, possibly Monday or Tuesday, a spokesman told The Associated Press. He spoke on condition of anonymity because he was not authorized to give his name to the media.

Meanwhile, Litvinenko's widow, Marina, sent a letter to Putin suggesting Russia has not cooperated fully with the British investigation.

In the Jan. 31-dated letter provided to AP, Marina Litvinenko told Putin that "if you do not make every effort to help the British authorities in the search for those guilty of this terrible crime, I can only suppose that you have something to hide."

A British Home Office official confirmed that Russian authorities had asked to come to Britain to investigate the death and police were considering the request. The official spoke on condition of anonymity because he was not authorized to speak about the subject.

Litvinenko, a former agent of Russia's Federal Security Service, the main successor agency of the Soviet-era KGB, fled to Britain and was granted asylum after accusing his superiors of ordering him to kill Russian tycoon Boris Berezovsky.

Berezovsky, a former Kremlin insider who became one of Putin's most prominent and influential critics, now lives in self-imposed exile in Britain. He is wanted in Russia on money-laundering charges that he claims are politically motivated.

Russian prosecutors have said they want to question Berezovsky. He said last month that he would answer questions but wanted his Russian interviewers to be searched by British police because he feared they might try to kill him.

Alex Goldfarb, an associate of Berezovsky, said the tycoon believes the Russian request to question more than 100 people in Britain is a "stunt" aimed to hamper the British probe. But he said Berezovsky is still willing to meet with Russian officials if provided adequate security.

Litvinenko accused Russian authorities of being behind a series of deadly bombings of apartment buildings in 1999 that stoked support for a renewed war with Muslim separatists in Russia's Chechnya region. Once in exile, he continued his criticism of the Kremlin and Putin.

He died in a London hospital Nov. 23. Doctors said he had been poisoned with polonium-210, a rare radioactive isotope.

In a deathbed statement, Litvinenko accused Putin of ordering his murder, an allegation the Kremlin has denied.

British investigators traveled to Moscow in December and sat in as Russian investigators questioned Andrei Lugovoi and Dmitry Kovtun. The pair met with Litvinenko in London on Nov. 1, hours before he reported feeling ill, but they have repeatedly denied any involvement in his death.

Russian Prosecutor General Yuri Chaika said last month that British investigators want to return to Russia to continue the investigation. He hinted they would only be permitted to do so if Russian officials were allowed to investigate in Britain.

Yuri Felshtinsky, co-author with Litvinenko of a book detailing claims that the Federal Security Service was behind the 1999 apartment bombings, alleged in an interview with the British Broadcasting Corp. on Sunday that the agency killed Litvinenko.