Turkey on Friday arrested 25 people for suspected links to the Gülenist Terror Group (FETÖ), the group behind the 2016 coup attempt.

Prosecutors in Ankara issued arrest warrants for a lieutenant and 48 sergeants who were found to have periodically and successively communicated with FETÖ's "covert imams" or senior operatives via pay phones. The operations in 22 provinces have so far resulted in the arrest of 25 of the suspects.

The suspects include one retired, 46 on-duty and two dismissed soldiers.

FETÖ and its U.S.-based leader Fetullah Gülen orchestrated the defeated coup of July 15, 2016, which killed 251 people and injured nearly 2,200.

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

Since the 2016 coup attempt, prosecutors have found that nearly 14,500 people used pay phones to communicate with the senior members of FETÖ. Around 13,500 of them were arrested in over 800 operations across the country. Some 5,000 of the detainees have been remanded in custody, while nearly 8,500 suspects were released, including those under judicial control.

FETÖ often resorts to this communication method to relay the messages of high-ranking members of the terrorist group to infiltrators. Authorities say the group's handlers contacted infiltrators via calls from pay phones at regular intervals and arranged secret meetings with them.