Interpol has joined the investigation into the poisoning of former Russian agent Alexander Litvinenko, the head of the organization's Russian office said on Tuesday.

British investigators arrived in Moscow last week to interview people who met Litvinenko around the time of his alleged poisoning in early November. Russian prosecutors have also opened a criminal investigation into Litvinenko's poisoning.

"Considering that law enforcement agencies of different countries are handling this, Interpol and its possibilities are certainly being used," Timur Lakhonin, chief of Interpol's Russian office, was quoted by the Itar-Tass news agency as saying.

"Interpol has been already engaged in the operative exchange of information between different countries," Lakhonin said.

Also on Tuesday, German authorities said that four people close to Litvinenko were in no danger of radiation contamination as first feared.

Marina W, the ex-wife of Dmitry Kovtun, her two children and her new boyfriend were given the all-clear after precautionary tests at a hospital on Monday, Gerald Kirchner of the Federal Bureau for Radiation Protection told a Bavarian television channel.

The four were previously feared to be contaminated with polonium 210 as Kovtun, a businessman, stayed in their apartment in Hamburg for five days before he flew to London to meet Litvinenko.

Kovtun is one of three Russians who met with Litvinenko at a London hotel on Nov. 1, the day before the former Russian agent became fatally ill.

He is being investigated for bringing polonium 210, the radioactive substance that killed Litvinenko, into Germany in late October, when he passed through the country on his way from Moscow to London.

Polonium 210, which is not harmful to the skin but lethal if ingested, breathed in, or enters the bloodstream through a wound, has been detected in the apartment of Kovtun's ex-wife and her mother's home.

Litvinenko died of radioactive poisoning late last month in London. Experts investigating his death have found radiation traces at a dozen locations and on two British Airways planes that flew the Moscow-London route.

Litvinenko, who was a strong critic of Russian President Vladimir Putin, accused the Kremlin of orchestrating his poisoning just before his death. Moscow vehemently denies the charge.

The former agent, who had been arrested several times, fled to Britain with his wife and son in November 2000 and was granted asylum. He became a British citizen last month.

(Xinhua News Agency December 13, 2006)