The investigation was being conducted in 62 provinces as part of a sustained crackdown against the network of U.S.-based preacher Fethullah Gulen. More than 250 people were killed in the failed putsch in July 2016. Gulen denies any involvement.

Istanbul prosecutors ordered the arrest of 258 suspects, with the serving personnel including four colonels, one lieutenant colonel, nine majors and 24 captains, Anadolu said. Prosecutors in the western Turkish city of Izmir sought the detention of 274 people, also mostly serving military personnel.

In the wake of the coup attempt, about 80,000 people were held pending trial and some 150,000 civil servants, military personnel and others were sacked or suspended. More than 20,000 people have been expelled from the Turkish military.