BERLIN/MOSCOW, December 9 (RIA Novosti) - Police in the German city of Hamburg on Saturday reported finding traces of radiation in places visited by a key witness in the murder case of former Russian intelligence agent Alexander Litvinenko.

Massive radiation checks are being carried out in Britain, Russia, and Germany as part of an international investigation into the murder of Litvinenko, who died in London November 23 of poisoning caused by radioactive substance polonium 210. He defected to the UK several years ago, and was known as a staunch critic of President Vladimir Putin.

No radiation has been detected in Russian spy-turned-businessman Dmitry Kovtun's Hamburg apartment, but his ex-wife's flat in the suburb of Pinneberg has proved contaminated.

Kovtun, who met with Litvinenko in London shortly before the exiled spy was taken to hospital and diagnosed with poisoning, is now reported to have been hospitalized with similar symptoms. His lawyer, however, has dismissed the reports about Kovtun's illness.

British detectives currently in Moscow for their probe into Litvinenko's murder spoke with Kovtun through Russian counterparts earlier this week. But they have still been unable to question Andrei Lugovoy, another key witness in the case, who went to see the defected spy in London together with Kovtun.

Western media suggested the polonium 210 used for poisoning Litvinenko might have been produced in the hotel room where Lugovoy was staying while in London. The contact has so far declined to comment.