A former business associate of former KGB officer Alexander Litvinenko today denied that he was involved in the poisoning.

Andrei Lugovoy, a business partner of Litvinenko who met him in London on November 1 at the Millennium Hotel in Mayfair shortly before Litvinkenko fell ill, insisted that the police were interviewing him as a witness.

In a telephone interview with The Associated Press, he said: "I am not regarded as a suspect, I am regarded as a witness, police are not accusing me of anything. As for all that is being said - it’s nothing but hysteria in the media."

He added: "I will respond to all my critics after the investigation is over."

Mr Lugovoy said he was undergoing tests at a Moscow clinic but declined to specify what he was being tested for. Media reports have said that Mr Lugovoi was being checked for radiation.

His comments came as Russian news agencies reported that Russian and British investigators were questioning another witness in the Litvinenko case.

Vyacheslav Sokolenko, who briefly saw Litvinenko in London on the weekend of November 1, was giving testimony to Russian prosecutors in the presence of visiting Scotland Yard officers, the ITAR-Tass and Interfax news agencies reported, citing unnamed sources close to the investigation.

Interfax, citing informed sources, said prosecutors also planned to conduct further questioning of another business partner, Dmitry Kovtun, who was also present at the November 1 meeting, on either Monday or Tuesday.

Russian officials have opened a criminal investigation into how Mr Kovtun came to be contaminated with radioactive poisoning. German police found traces of radiation in Hamburg, where he spent several days on his way from Moscow to London in late October.

Litvinenko, 43, died on November 23 in London after being poisoned with the rare radioactive element polonium-210. In a deathbed accusation he blamed Russian President Vladimir Putin - an allegation the Kremlin strongly denied.

Kremlin officials have already warned British police officers investigating the case that they cannot arrest anyone in Russia and that no-one will be extradited back to the UK to stand trial.

It is thought that British police officers could be planning to travel to Germany to conduct further inquiries into the murder.

Scotland Yard is still awaiting the results of the post mortem examination on Litvinenko’s body, which was carried out two weeks ago. They are unlikely to be known until next week.