Ankara police have detained 11 people working in several Turkish banks over their alleged use of a mobile phone messaging app used by the Gülenist Terror Group (FETÖ), prosecutors said Thursday.

They are among the 20 employees of Turkey's Central Bank, Bank Asya, Iller Bank and Development Bank of Turkey, against who the Ankara Chief Public Prosecutor's Office issued a detention decision, for suspected ties to FETÖ, which the Turkish government accuses of orchestrating last July's coup.

Except FETÖ-linked Bank Asya, which was seized in 2015 due to its deteriorating financial condition amid terror probes, all banks involved in the probe are public banks.

They are all accused of using the ByLock app that authorities say was used exclusively by FETÖ, which expanded its infiltration into the state, from law enforcement to judiciary and the army, thanks to the importance it attached to secrecy and disguise.

The encrypted messaging app was cracked by Turkish security agencies, prompting FETÖ members to switch to the WhatsApp messaging service.

Still, security forces were able to identify tens of thousands of FETÖ suspects who corresponded via Bylock. As a result, almost daily operations are being carried out against Bylock users.

The 20 suspects served with detention warrants in Thursday's operations have been fired from their jobs.

In a separate operation led by the Ankara police, 42 military officials were arrested for alleged links to FETÖ, of which 17 were taken into custody.

The operation was spread across 25 provinces, including Ankara, Istanbul, Izmir, Erzurum and Malatya.

On May 31, the prosecutor's office had issued arrest warrants against 60 soldiers, who were on duty at the Turkish Military Academy on the night of the coup.

The July 15 coup attempt, which Turkey says was masterminded by U.S.- based Fetullah Gülen, saw 250 people martyred and 2,200 wounded.

Ankara 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.

In the wake of the coup attempt, tens of thousands of FETÖ suspects have been arrested, including many in the armed forces, police, the judicial system, and education and business sectors.