German police have arrested a 31-year-old Turkish man suspected of providing information on Kurds living in Germany to Turkish intelligence agencies, the German federal prosecutor's office says.
The arrest could exacerbate tensions between NATO partners Germany and Turkey, which has accused Berlin of harbouring militants from the Kurdistan Workers Party (PKK) - fighting a three-decade-old armed campaign for autonomy - and far-leftists of the DHKP-C, which has carried out attacks in Turkey.
German officials reject that claim.
The prosecutor's office said in a statement on Friday that police had arrested the man, identified only by the initials MS, in Hamburg on Thursday and searched his home.
"The accused is strongly suspected of working for the Turkish intelligence agency and providing information about Kurds living in Germany, including their whereabouts, contacts and political activities," it said.
The prosecutor's office had no immediate comment about the man's links to Ankara and how long he had been living in Germany.
German Foreign Minister Frank-Walter Steinmeier criticised Turkey's arrest of Kurdish opposition leaders last month, saying Ankara had a right to fight terrorism but could not use it to justify gagging opponents.
Ties between the two NATO allies have been strained since the German parliament voted in June to declare the 1915 massacre of Armenians by Ottoman forces a genocide. The situation has deteriorated with growing German concerns about Turkey's mass arrests and suspensions since a failed July coup attempt.
European countries have criticised Turkey's post-coup crackdown, but remain wary of jeopardising Ankara's support for a deal with the European Union that has helped reduce the number of migrants reaching Europe to some 380,000 this year from over 1 million last year.