A married couple have gone on trial in Germany for spying in what German media say is one of the most intriguing cases since the end of the Cold War.
The couple, codenamed Andreas and Heidrun Anschlag, are said to have settled in then West Germany on false passports some 25 years ago.
They are accused of feeding information to the former Soviet Union and then Russia since then.
The couple, who were arrested in October 2011, deny the charges.
But a spectacular trial followed by a conviction could sour bilateral relations, German media warn.Wireless transmitter
The couple were arrested at their home in the western town of Marburg in the early morning of 18 October 2011.
At the time, prosecutors allege, Mrs Heidrun was sitting in her study in front of a wireless transmitter that was receiving encoded messages on a shortwave frequency and was hooked up by cable to a computer,reports the German news website Spiegel Online.
According to the charge sheet, the suspects are accused of passing confidential documents bought from a Dutch foreign ministry official and passing them to Russian intelligence services, German newspaper Die Welt reported.
The documents reportedly included secret information about Nato operations.
On the sidelines of the trial in Stuttgart a defence lawyer confirmed that the suspects were Russian citizens, AFP news agency reported.
Prosecutors say they posed as Austrian citizens of South American descent after arriving in Germany in 1988 and 1990.
The BBC's Stephen Evans in Berlin that there is speculation about whether the authorities were alerted to the German couple by the same person - whoever that may be - who told the FBI in the United States about the Russian spy ring uncovered there involving Anna Chapman. She had admitted to spying and was then deported to Russia where she has since become a celebrity.
One intriguing footnote about the case, our correspondent adds, is that Russian President Vladimir Putin worked for the KGB in Dresden through the 1980s when the couple are accused of beginning to spy for that very organisation.
If they did, many would want to know if Mr Putin knew, says our correspondent.
The trial is expected to last until June.