A tip-off from a friendly intelligence service led to the arrest of a German armed forces translator this week on suspicion of spying for Iran, according to reports on Thursday.

A friendly intelligence service warned the German military that it had an Iranian spy in its ranks as long ago as 2017, according to Spiegel magazine. The report does not name the intelligence service involved.

The warning contained no information about the identity of the alleged spy, or even which unit of the military he was serving in. German military intelligence began a laborious search to identify him, culminating in this week’s arrest.

A 50-year-old German citizen of Afghan heritage named only as Abdul Hamid S was held on Tuesday on suspicion of passing classified information to Iran for a number of years.

Abdul Hamid S, who is a German citizen, was based at a barracks in the Rhineland region where he worked for an electronic warfare unit translating Taliban signals intercepted by German troops serving with international forces in Afghanistan.

German investigators identified him when they noticed his suspicious travel patterns. He made a series of trips to European cities which coincided with visits by a known Iranian intelligence operative.