120 high-ranking police officers were detained and arrest warrants were issued for 46 others for using ByLock, an encrypted instant messaging app known to be used by members of the Gülen Terrorist Group (FETÖ) for internal communication in a nationwide operation on Friday morning.

The operation aims to target a total of 166 officers, a police official said, adding authorities were continuing to look for the remaining suspects. Those detained or sought were police employees, including 13 police chiefs, 114 ranking officers and 39 regular officers.

The operation was focused on Istanbul police headquarters but simultaneous raids were carried out in 35 provinces.

The smartphone app is believed to have been cracked by Turkish security agencies before the defeated coup and reportedly identified tens of thousands of members of FETÖ, which the government has said was behind the attempted takeover.

The codes of Bylock were broken in August, resulting in 60,000 members being uncovered. Another encrypted messaging app, Eagle, was also deciphered by intelligence officers recently.

Prosecutors say that Bylock was popular among Gülenists as a secretive form of communication from 2013 to 2015. Various ministries have since launched an investigation into workers who allegedly used Bylock by actively suspending and terminating app users who were found to be active members of FETÖ.

The failed July 15 coup attempt, which left 241 people dead and nearly 2,200 injured, was organized by followers of Gülen, who has lived in self-imposed exile on a 400-acre property in the foothills of the Pocono Mountains in Pennsylvania since 1999. Gülen has led a long-running campaign to overthrow the state through infiltration of Turkish institutions, particularly the military, police and judiciary.