(CNN) Turkey may be using the multinational police organization Interpol to hunt down political opponents of the country's president abroad, a German government spokesman said Monday.

The accusation follows the arrest and release of a prominent Turkish-German writer, the latest sign of the deterioration of ties between Turkish President Recep Tayyip Erdogan and Germany over what Germany perceives to be Turkey's interference in its political affairs.

A 60-year-old critic of the Erdogan government, Dogan Akhanli was born in Turkey but has German citizenship. He was detained Saturday while on holiday in Spain. A resident of the western German city of Cologne since 1992, he was released Sunday after a court hearing, but on the condition that he remain in Madrid, according to his lawyer, Ilias Uyar.

The warrant for his arrest was issued four years ago; it is unclear why it has been acted upon now. The reason for Akhanli's arrest was not immediately given, but Akhanli has written in the past about the mass killing of Armenians in Turkey in 1915. The subject is a controversial one in Turkey, which rejects the view of much of the international community that the killings constituted genocide.

Interpol calls itself the world's largest police organization. "With 190 member countries, its primary role is to assist law enforcement agencies around the world in combating all forms of transnational crime and terrorism."