Germany's top security official has defended his ministry's confidential assessment of Turkey as "the central platform of action for Islamist groups" in the Middle East, which was leaked last week to the public.

Interior Minister Thomas de Maiziere told Bild am Sonntag newspaper Sunday that "what has been in the media about the report is only a small excerpt about the current state of the country, and that is quite complicated."

De Maiziere says that Turkey is a fellow NATO member, and an "important partner" in the migrant crisis and fight against terrorism.

But he adds that Germany sees that many measures taken in the wake of the recent coup attempt as "disproportionate" and is in regular dialogue with Ankara.