Russia began a spying inquiry today into the murder of the dissident FSB agent Alexander Litvinenko in a move apparently calculated to heighten tensions with Britain.

The Federal Security Service (FSB) said that it had opened an espionage investigation as a result of claims made by Andrei Lugovoy, the man whom Britain wants to extradite on a charge of murder.

Mr Lugovoy declared his innocence at a press conference in Moscow last month and accused the British Secret Service, MI6, of involvement in killing Mr Litvinenko.

Mr Lugovoy, a former KGB bodyguard in the Kremlin, also alleged that MI6 tried to recruit him to gather compromising material on President Vladimir Putin. He claimed that Mr Litvinenko and his patron, the exiled Russian billionaire Boris Berezovsky, were employed by MI6.

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BACKGROUND

• Lies and the spies: I must have justice

• Shadowy ex-KGB major takes cover

• Of course the Russians did it. They’re the experts

• The Litvinenko File

• Litvinenko was told that he was marked for death

Related Links

• No 10 plan for Litvinenko murder trial

• Blair talks of ‘deep freeze’ after Putin talks

• Suspect: MI6 had a hand in death of Litvinenko

Mr Lugovoy pledged to provide Russian prosecutors with evidence to support his claims. Mr Berezovsky and Mr Litvinenko's widow Marina have rejected the allegations.

The FSB announced the criminal inquiry in a terse one-line statement that gave no indication of who it suspected of spying. It confirmed only that the investigation had been triggered by Mr Lugovoy's statement.

However, the clear implication is that Russia is taking Mr Lugovoy's claims seriously and may be preparing to reject British demands for cooperation in the case by accusing London of a spying campaign against the Kremlin.

Mr Putin dismissed the Scotland Yard inquiry into Mr Litvinenko's death as "stupid, stupid nonsense" in an interview with The Times on the eve of this month's G8 summit.

The British Embassy in Moscow responded to the latest development by renewing its call for Russia to assist in bringing Mr Lugovoy to trial in London. An embassy spokesman said: "The Litvinenko affair is a criminal matter and not an issue of intelligence. A British citizen was killed in London and UK citizens and visitors were put at risk.

"We are seeking and expect full cooperation from the Russian authorities in bringing the perpetrator to face British justice."

Mr Lugovoy refused to comment on the FSB's announcement but said that he was "actively cooperating with Russian investigators, including in questions of providing for the security of our state".

Britain has asked Russia to extradite Mr Lugovoy after the Crown Prosecution Service formally accused him of murdering Mr Litvinenko last month. The Prosecutor-General's Office insists that extradition would be contrary to Russia's Constitution, but has not ruled out a trial in Moscow.

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