MOSCOW - The chief prosecutor said Tuesday Russia would not allow the extradition of possible suspects in the poisoning of a former KGB agent in Britain and he dismissed as "nonsense" allegations by another ex-security officer of a death squad for Kremlin critics.

This undated file picture shows Soviet policemen standing guard in front of the KGB building in Moscow, with a portrait on Vladimir Lenin on it. Russia laid down strict ground rules to visiting British counter-terrorism police probing the poisoning of former spy Alexander Litvinenko, and ruled out the extradition of any suspects. [AFP/File]

Prosecutor General Yuri Chaika also confirmed that a potential central witness in the case, another former agent who met with Alexander Litvinenko in London on Nov. 1, the day Litvinenko believed he was poisoned, had been hospitalized.

Related forum:  Poisoned former KGB spy dies in London  Poisoned spy blames Putin for death  Spy death figure tested for radiation  Radiation found on jets in spy probe  Former spy's wife positive for radiation  Friend names suspect in spy case  Poisoning case damaging UK-Russia ties  Contact says secret Russian groups poisoned ex-spy

Litvinenko, 43, died Nov. 23 in London, and doctors found the radioactive isotope polonium-210 in his body. In a deathbed statement, he blamed President Vladimir Putin for the poisoning. The Kremlin has vehemently denied the accusations.

Chaika said Russian prosecutors would fully cooperate with Scotland Yard, which has sent a team of British investigators to Moscow.

He said all the figures in the case whom the British investigators had requested to see are being interrogated by Russian prosecutors in presence of the British officers. "It is we are who are doing all the interrogating. They only attend that, it cannot be otherwise on the territory of our state," Chaika said.

Chaika's comments came a day after Foreign Minister Sergey Lavrov warned that continued suggestions of Kremlin involvement in Litvinenko's death could damage relations with Britain.

In televised comments, Lavrov said he had spoken with British Foreign Secretary Margaret Beckett "about the necessity to avoid any kind of politicization of this question, this tragedy ¡ª the death of person is always a tragedy - and the necessity to avoid speculation on this subject."

Chaika confirmed that Andrei Lugovoi, the ex-agent who met with Litvinenko Nov. 1, had been hospitalized and said the British officers could talk to him with doctors' permission. "Everything will depend on the doctors' opinion," he said.

Chaika also insisted that there would be no extradition of any Russian suspects in the poisoning, saying "they are citizens of Russia and the Russian constitution makes that impossible."

Turning to another figure in the Litvinenko case, former security officer Mikhail Trepashkin, who is now serving a four-year prison sentence after being convicted of divulging state secrets, Chaika said the British investigators would not be allowed to visit him.

Trepashkin has claimed in a letter from prison that he had warned Litvinenko several years ago about a government-sponsored death squad that intended to kill him and other Kremlin opponents.

Chaika dismissed Trepashkin's allegations as "nonsense," but said added that if substantial facts are collected to support Trepashkin's evidence, Russian prosecutors could consider allowing British police to interview him.

The case has further strained already tense relations between Russia and Britain, which has infuriated the Kremlin by giving asylum to tycoon and fierce Kremlin critic Boris Berezovsky and Chechen rebel envoy Akhmed Zakayev in addition to Litvinenko, a former Federal Security Service officer turned Kremlin critic.