Turkey has ordered the detention of 304 military personnel in an operation targeting supporters of the Muslim preacher that Ankara says was behind a failed coup in 2016, state-owned Anadolu news agency said on Tuesday.

Operations targeting the network of US-based cleric Fethullah Gulen have continued under a four-year-long crackdown since the attempted coup in July 2016. 

Gulen, the Turkish Islamic scholar, denies involvement in the putsch attempt, in which about 250 people were killed.

Tuesday's operation was initiated by the prosecutor's office in the western coastal province of Izmir and was spread over 50 provinces, Anadolu said in a statement.

The suspects, including five colonels and 10 captains, most of them on active duty, were believed to be in contact with people with links to Gulen's network, Anadolu said.

Since the coup attempt, about 80,000 people have been held pending trial and some 150,000 civil servants, military personnel and others have been sacked or suspended. 

More than 20,000 people had been expelled from the Turkish military alone.

Reuters