A key witness in the investigation into the radiation death of former Russian intelligence agent Alexander Litvinenko denied involvement in the poisoning today, saying he is being unjustly accused in the media.

Experts have found minor traces of radiation at the British Embassy in Moscow but they presented no health risk to the public, an embassy spokesman said today.

British police investigating the poisoning death of a former KGB agent have officially requested assistance from their Russian counterparts, prosecutors said, as officers arrived in Moscow amid rising diplomatic tensions.