A German citizen has been arrested on suspicion of being a double agent and spying for the United States.

The 31-year-old man, who is understood to work for Germany’s own BND intelligence service, is accused of spying on a German parliamentary inquiry into revelations made by former U.S. intelligence contractor Edward Snowden.

German government spokesman, Steffen Seibert, said: “This is a very serious incident. That is why the Federal State Prosecutor has become involved. Spying for foreign intelligence services is not something that we treat lightly. But it is a matter for the Federal State Prosecutor and the investigating Federal Criminal Office now – and it is in very good hands.”

According to German media, the man was originally arrested on suspicion of making contact with Russian intelligence, but then confessed he was in fact spying for the Americans.

Social Democrat Thomas Oppermann said: “Under no circumstances is it justifiable that a world power or a country -especially not our friends, the United States – would recruit BND employees to spy on the work of the German parliamentary NSA investigation committee.”

The incident is the latest in a string of spying scandals that have strained relations between Berlin and Washington.

They include revelations that the US National Security Agency was monitoring Chancellor Angela Merkel’s mobile phone and carrying out mass surveillance of German citizens.

If the case is proven it could turn into the biggest scandal involving a German – American double agent since the war.