UPDATE - Nearly 650 FETO suspects arrested in nationwide op.

UPDATES TO ADD ARREST OF 641 FETO SUSPECTS; MODIFIES HEADLINE, DECK, LEDE

By Serdar Acil, Baris Kilic and Orhan Onur Gemici

ANKARA (AA) - At least 641 suspects have been arrested in a nationwide operation on Tuesday against Fetullah Terrorist Organization (FETO) suspects in a probe related to a leaked 2010 police exam paper.

Judicial sources told Anadolu Agency that Turkish security forces arrested 641 FETO suspects out of a total of 1,112 sought in Tuesday's counter-terrorism operation.

Turkish police are looking for the remaining suspects.

The suspects are believed to have exam questions before sitting for the sub-inspector test, said the judicial sources, who spoke on condition of anonymity due to restrictions on speaking to the media.

They leaked the exam paper in a bid to infiltrate the police force, the sources added.

The probe is being led by Ankara Chief Public Prosecutor's Office with simultaneous nationwide operations launched by police.

FETO and its U.S.-based leader Fetullah Gulen orchestrated the defeated coup of July 15, 2016, which left 251 people martyred and nearly 2,200 injured.

Ankara accuses FETO of being behind a long-running campaign to overthrow the state through the infiltration of Turkish institutions, particularly the military, police, and judiciary.