Commando unit raids home of married couple in Marburg, in case that may add to strain on German-Russian relations

A married couple have been arrested in Germany on suspicion of spying for Russia. It is believed to be the first such case on German soil since the cold war.

The alleged spies are suspected to have worked undercover for the Russian secret service for more than 20 years. A commando unit from the Federal Office of Criminal Investigation (BKA) raided their home in Marburg last week.

Germany's public prosecutor confirmed the arrests, saying the couple were suspected of "secret service agent activity" and of using false documentation.

"The accused are strongly suspected to have been actively working for a foreign intelligence service for a long time in the Federal Republic of Germany," said the prosecutor in a statement. A spokesman refused to answer any questions but confirmed that the couple had not yet been indicted on any charges.

The alleged spies appeared before a judge in Karlsruhe last week and were remanded in custody.

Analysts said the new spy scandal would put pressure on already strained German-Russian relations. Last month the announcement by Vladimir Putin, himself a former KGB agent, that he was to run again for the Russian presidency drew criticism in Germany and beyond.

The prosecutor's office would not reveal the nationalities of the couple, nor the countries for which they were suspected of working. Der Spiegel identified the pair as 51-year-old Heidrun A and her husband, Andreas, 45, both of whom were suspected to have begun spying for the KGB in 1988, before the Berlin Wall fell. Since reunification they are alleged to have answered to the SVR, Russia's foreign intelligence service, a successor organisation to the KGB.

Their identity papers – suspected to be fakes – claimed Andreas was born in Argentina and Heidrun in Peru, but both had Austrian passports, Der Spiegel reported.

The magazine said inquiries with the Peruvian and Argentinian authorities suggested the couple had lied about their birthplaces and that although Andreas claimed to speak only English, Spanish and German, he spoke with a Russian accent.

It reported that the woman was listening to coded messages on a shortwave radio linked up to a computer when the commandos stormed in. Her husband was arrested in Balingen, in the southern German state of Baden-Württemberg, where he worked.

Focus magazine said the pair may have had ties to an exposed Russian sleeper cell network in the US that included Anna Chapman, the spy turned celebrity.

The Russian embassy in Berlin said it had not been contacted by the BKA to inform them of the arrest of any Russian citizens accused of espionage. The Austrian embassy in Berlin said it had also not yet been contacted by the German authorities in connection with the case.

In Russia, officials refused to comment on the case. The Kommersant newspaper reported that the alleged spies lived in a private home in a "quiet and respectable" area of the Michelbach quarter of Marburg. A neighbour told the paper that the couple "practically never spoke to anyone and lived a very secluded life".

The neighbour added: "They weren't members of any local organisations or clubs and they didn't attend any local festivities. After their arrest we realised that none of us neighbours had pictures together with them." Heidrun was often seen leaving the house in the morning with a large sports bag although she didn't frequent the local sports club, the neighbour said. Der Spiegel claimed investigators sawed open a tennis racket found in the house while looking for evidence.

Kommersant reported that the couple had a daughter who was studying at a local university.

In another recent spy case, a court in Munich jailed Harald S, 54, an Austrian citizen, in March for passing information about a helicopter manufacturing firm to the SVR in exchange for at least £6,500.

Last summer, Thomas de Maizière, Germany's then interior minister, presented an intelligence report which concluded that "states like Russia and China are actively operating espionage in the areas of the economy, science and research".

Jana Kobzova, an analyst at the European Council on Foreign Relations, said: "This is not a particularly rosy time in the German-Russian relationship, and this will definitely spoil things a little bit more. Germany maintains a policy of engagement, rather than isolation, with Russia and this won't change that.

"But coming as it does after Putin's announcement - given how much effort Angela Merkel put into meeting and working with Dmitry Medvedev - and German energy companies talking about arbitration with Gazprom over energy prices, it is certainly not helpful."