German prosecutors are investigating whether two Russian dissidents living in Berlin have been poisoned.
Earlier this month, the German weekly Focus reported that doctors had detected high levels of mercury in the blood of Viktor and Marina Kalashnikov.
He was a former colonel in the KGB while she is a historian and both have been critical of the Kremlin.
In 2006, former Russian agent Alexander Litvinenko was murdered by radioactive poisoning in London.
British investigators suspect former KGB agent Andrei Lugovoi is behind his murder.
A spokesman for the public prosecutors' office in Berlin confirmed that an investigation had been opened into whether the Kalashnikovs have been deliberately poisoned.
"It is being carried out by a department dealing with politically motivated crimes," the spokesman told AFP news agency. BBC News
