Turkey ordered the arrest of more than 100 soldiers and former military students over suspected links to the network of the US-based Muslim cleric accused of orchestrating a 2016 attempted coup, prosecutors and state media said on Friday.

Police operations targeting supporters of cleric Fethullah Gulen have been carried out regularly since the failed putsch and have recently gained momentum. Mr Gulen denies involvement in the coup attempt, in which 250 people were killed.

The Istanbul chief prosecutor's office said it ordered the arrest of 50 suspects - six of them officers and the rest military academy students expelled after the putsch - in an investigation into people linked to Mr Gulen in the military.

This operation, spread across 16 provinces, was focused on calls made over fixed phone lines, the statement said.

In the southern Adana province, prosecutors ordered another 52 soldiers arrested, 42 of them serving, in an operation spread across 20 provinces, state-owned Anadolu news agency reported.

It said colonels, majors, lieutenants and other serving officers were facing arrest over pay phone calls they made to other alleged Gulen-linked people. Many suspects have already been detained, it added.

More than 77,000 people have been jailed pending trial, while 150,000 civil servants, military personnel and others have been sacked or suspended from their jobs as part of the post-coup purges. Widespread operations are still routine.

Rights groups and Turkey's Western allies have voiced concerns over the crackdown, saying President Tayyip Erdogan has used the abortive putsch as a pretext to quash dissent. The government has said the security measures were necessary due to the gravity of the threat Turkey faces.