Turkish authorities on Monday ordered the arrest of 249 past and present foreign ministry personnel suspected of ties to the group blamed for a failed 2016 coup, the prosecutor's office said.
At least 78 have already been detained, the office in the capital Ankara said.
The latest crackdown is part of a probe in 42 cities into alleged irregularities in the foreign ministry entrance exam in favour of members of a movement led by US-based Muslim preacher Fethullah Gulen.
The suspects joined the foreign ministry between 2010 and 2013, according to the prosecutor's office.
Fourteen are currently serving in the ministry, while the rest had already been removed from their posts, a judicial source told AFP.
Ankara blames Gulen and his followers for orchestrating a failed coup in 2016 aimed at unseating President Recep Tayyip Erdogan.
The movement denies the allegations and insists it is a peaceful group promoting education and moderate Islam.
Tens of thousands of public sector workers, including teachers, judges and soldiers, have been sacked or suspended since the attempted coup.
Turkish authorities say it has been necessary to remove Gulen's "virus" from state institutions, but activists and Western allies have strongly criticised the magnitude of the crackdown.