The Turkish foreign ministry on Tuesday said it had called in the German envoy to protest comments by Berlin's foreign intelligence chief expressing scepticism that US-based Islamic preacher Fethullah Gulen was behind the July 15 failed coup.
In an interview with Der Spiegel published on Saturday, Bruno Kahl said Ankara had repeatedly tried to convince Berlin that Gulen was behind the coup "but they have not succeeded".
The foreign ministry said in a statement that the German charge d'affaires in Ankara was "invited" to the foreign ministry to hear a protest from Turkey.
The statement said the link between Gulen and the coup was well established and Kahl's comments showed "the mentality behind Germany's tolerant and protective attitude" towards the group.
Gulen denies any links to the coup.
Tensions are running high between Berlin and Ankara after German authorities refused to allow some Turkish ministers to campaign in the country for a 'yes' vote ahead of the April 16 referendum on handing President Recep Tayyip Erdogan an executive presidency.
The dispute has been exacerbated by Erdogan accusing Berlin of behaving like Nazi Germany.