An Istanbul court on Friday remanded 17 Turkish journalists in custody over links to the US-based preacher Fethullah Gulen who is blamed for this month's failed coup, charging them with membership of a "terror group".

Twenty-one journalists had their cases heard by the court, with four being freed and 17 placed under arrest ahead of trial, the state-run Anadolu news agency said.

Those held include the veteran journalist Nazli Ilicak as well as the former correspondent for the pro-Gulen Zaman daily Hanim Busra Erdal, it added.

Among the four freed was prominent commentator Bulent Mumay.

Those held have all been charged with "membership of a terror group". Turkey considers Gulen's organisation to be a terror goup that was behind the July 15 coup, charges he fiercely denies.