British detectives investigating the poisoning death of a formerKGB agent have ended their work in Moscow, as a key witness in the case faced a second round of questioning Monday, Russian news agencies reported.

Scotland Yard investigators, who have interviewed at least six people since arriving in the Russian capital two weeks ago to investigate the death of Alexander Litvinenko, could leave for London as early as Tuesday, the Interfax news agency reported. The report cited sources close to the investigation.

Neither British nor Russian officials would comment.

Dmitry Kovtun, a businessman and former agent who met with Litvinenko in a London hotel on Nov. 1, the day Litvinenko fell ill, was questioned a second time by British detectives and Russian investigators.

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Kovtun, who is undergoing treatment for radiation poisoning at a Moscow clinic and was questioned by Scotland Yard detectives earlier this month, said he gave "exhaustive" answers during Monday's meeting, according to the RIA-Novosti news agency.

Kovtun did not elaborate on his interrogation, citing a pledge not to divulge its details.

Litvinenko died Nov. 23 in London after being poisoned with polonium-210 and in a deathbed accusation blamed President Vladimir Putin — an allegation the Kremlin vehemently denied.

Among the other people questioned by British detectives were his business associate, Andrei Lugovoi, who also met with Litvinenko on Nov. 1.

German authorities have found traces of polonium-210 in several locations in Hamburg visited by Kovtun just before he flew to London for the Nov. 1 meeting. Interfax said the second questioning of Kovtun was prompted by the developments in Germany.

Traces of polonium-210 have now been confirmed in the Hamburg apartment of Kovtun's ex-wife, where he spent two nights in late October, and the car that picked him up from the Hamburg airport when he arrived from Moscow.

German prosecutors are investigating Kovtun on suspicion that he may have illegally handled radioactive material. They have left open whether the radioactive trail meant he might have been involved in Litvinenko's poisoning, saying that he may have been a victim or could have been involved in procuring the polonium.

Germany's ambassador to Moscow, Walter Schmid, said Monday that German investigators were considering whether to travel to Russia to continue the probe, ITAR-Tass and RIA Novosti reported.

Lugovoi, Kovtun and Vyacheslav Sokolenko, a third associate who was in London with them on the weekend of Nov. 1, have denied involvement in Litvinenko's death.

The incident has strained relations between Moscow and London.

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