Prosecutors in Germany have opened an investigation into whether two Russian exiles living in Berlin were poisoned.
The BBC reports the inquiry is being carried out by an official department dealing with political crimes.
The German weekly Focus reported earlier this month that doctors have detected dangerously high levels of mercury in former KGB Colonel Viktor Kalashnikov, 58, and his wife Marina Kalashnikov, a historian.
The magazine said both have health problems, with Marina losing half of her hair and Viktor considerable weight. Medical experts have recommended that the couple undergo further tests and be watched closely.
The couple have worked as freelance journalists since the late 1990s. They arrived in Berlin in September.
Focus reported that doctors at Berlin's Charite hospital found 53.7 microgrammes of mercury per litre in his blood and 56 mg/litre in her's.
"The maximum safe level is between one and three microgrammes of mercury in a litre of blood," the magazine quoted a toxicologist at Charite, as saying.
In 2006, Alexander Litvinenko, a dissident Russian spy, was murdered by radio-active poisoning in London.