German authorities have opened an investigation into 20 Turkish nationals who are suspected of conducting espionage activities on followers of Islamic cleric Fethullah Gulen in Germany, local media reported Thursday.

Axar.az reports that the 20 Turkish nationals, along with several unknown persons, are suspected of spying on Gulen's followers in Germany at the request of Turkish government, the Die Welt newspaper reported, citing a reply on the matter, obtained by the newspaper, of the German government received by a Die Linke party lawmaker.

The "unacceptable careless approach" of the government toward the Turkish-Islamic Union for Religious Affairs (DITIB) resulted in spies' ability to return to Turkey and avoid criminal prosecution, Die Linke lawmaker Sevim Dagdelen told the newspaper.