RUSSIAN prosecutors investigating the poisoning of Alexander Litvinenko, the former spy, want to travel to London to question a billionaire Russian exile and a Chechen associate.

The move is likely to further strain relations between Russia and Britain, which have been undermined by allegations that the FSB, the former KGB, might be involved in the killing. Russian authorities are also suspected of disrupting the BBC Russian service’s coverage of the murder.

The Russian investigators’ targets are Boris Berezovsky, a billionaire businessman who employed Litvinenko and is a long-standing critic of Vladimir Putin, the Russian president, and Akhmed Zakayev, a Chechen exile the Russians have wanted to extradite on terrorism charges, which he denies.

“There is no doubt that we will demand to question Berezovsky and Zakayev,” said a source close to the Moscow inquiry. “They both knew Litvinenko and could hold vital information.”

Russian investigators are likely to want to question Berezovsky about his links to Andrei Lugovoi, a key witness and possible suspect. Lugovoi had previously worked for Berezovsky, and it is understood the oligarch was considering employing him as a security adviser.

Zakayev was a close friend of Litvinenko. He accused the Moscow authorities of launching a black propaganda campaign over the former spy’s murder. “One [Moscow] version is that Mr Berezovsky killed Litvinenko because it was in his interests. It’s an absurd allegation,” he said.

The Home Office has refused previous requests from Moscow for the extradition of Berezovsky and Zakayev. The Moscow intervention will be viewed by critics of the regime as a crude tactic to divert attention from the Kremlin.

The threat of a diplomatic row between London and Moscow comes amid developments in the investigation. These include:

• Traces of polonium are reported to have been found in a cup and a dishwasher at the Millennium hotel in Mayfair, where Litvinenko had a meeting on the day he is believed to have been poisoned.
• Police in Hamburg, Germany, yesterday found radiation in apartments linked to Dmitry Kovtun, one of the three businessmen who met Litvinenko at the Millennium hotel on November 1. A German civilian jet was also tested for contamination.
• Moscow authorities have been accused of a misinformation campaign after it was reported that Kovtun had slipped into a coma on Friday. Kovtun denied the report this weekend in a telephone conversation with The Sunday Times.
• Mikhail Trepashkin, who is detained in Russia and who had warned Litvinenko his life was in danger, has been moved to a high-security jail. He will not be allowed to speak with British investigators.
• New tests indicate that Mario Scaramella, one of Litvinenko’s associates, is free of polonium contamination, despite being initially told he had been given 10 times the lethal dose. ()

Litvinenko’s friends believe he was assassinated by his former employer, the FSB. They are compiling files on previous cases that they now believe may be linked to polonium, including the deaths of two Chechen leaders in prison and that of one of Putin’s former bodyguards who died of “an unexplained illness”. The Kremlin has said it is “complete nonsense” to link these deaths to polonium.

Speculation about the possible role of the Kremlin has angered Russian authorities. It was reported yesterday that the Russians were suspected of disrupting the BBC’s Russian service FM broadcast in Moscow and St Petersburg at the height of the coverage of the Litvinenko poisoning.

There is also suspicion that the Kremlin might be orchestrating a campaign to discredit Litvinenko.

There are also reports that the Russian authorities are suspected of orchestrating a campaign of harassment against Tony Brenton, Britain’s ambassador in Moscow. Brenton has been targeted by Nashi, a nationalist youth movement linked to the Kremlin, since he gave a speech to the Russian opposition in July.

While Tony Blair is anxious that relations with Moscow do not suffer irreversible damage in the affair, Russian dissidents insist he adopts a tougher line. Vladimir Bukovsky, the leading Russian dissident in London, said: “We expect the British government to respond properly. Instead, we hear that our so-called prime minister told his colleagues that the priority is to retain good and friendly relations with Russia.

“What is this? A licence to kill? An open invitation to come and murder anyone Russia wishes as long as we have positive relations. Prime minister, you are wrong. Your prime duty as prime minister is to defend the citizens of this country and its sovereignty.”

British detectives in Moscow were still waiting to interview Lugovoi yesterday. He was due to be interviewed on Tuesday, but has not yet been made available by the Russian authorities .

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