The German Federal Police have arrested a married couple on suspicion of spying for Russia's foreign intelligence service for over two decades, according to reports in the German media.

­The Federal Prosecutor’s Office says the two were arrested on Tuesday by the GSG-9 special operations team, an elite division of the German police.

The pair were arrested separately, with one being picked up in the city of Baligen in Baden-Wuerttemberg state in the south-west of the country, while the other was detained in Marburg in the state of Hesse, which is to the west of central Germany.

Police reportedly walked in on the woman while she was listening to encoded radio transmissions.

The German news weekly, Der Spiegel, said that according to the authorities the man and the woman – referred to only as Andreas A. and Heidrun A. – had been working in Germany as Russian spies since the days when the KGB, the Soviet Union's spy agency, was operating in the country during the Cold War.

According to documents the couple both hail from South America, the man from Argentina and the woman from Peru, although both had Austrian passports.

However, inquiries made by German authorities in South America confirmed that the passport data had been falsified.

The couple allegedly moved to West Germany in 1988. Apparently, Andreas A. and Heidrun A. have been working all across Europe, with Germany serving as their base. It is thought they could have been playing a linking role between other agents and Moscow, media reports suggest. Also, according to Der Spiegel, Andreas A. speaks with a Russian accent, though he claims he knows only German, English and Spanish. Both have denied all charges.

It is not known what the alleged spies' target was, Der Spiegel says.

It is the first time undercover foreign agents have been found in Germany since the county was reunified in 1990, Der Spiegel stresses.

Police began investigating the couple after a Russian spy ring was uncovered in the United States last year.