Turkey on Monday, January 30 opened the biggest trial yet over the failed July coup aimed at ousting President Recep Tayyip Erdogan, trying 270 suspects including, in absentia, the alleged mastermind Fethullah Gulen, AFP reports.

The suspects, 152 of whom are in pre-trial detention, include ex high-ranking military officials like former Aegean Army Command Chief of Staff Major General Memduh Hakbilen, the state news agency Anadolu reported.

Also going on trial was ex-NATO Land Commander Chief of Staff Major General Salih Sevil.

The "number one" suspect is US-based Islamic preacher Gulen who is charged with ordering the failed July 15 coup, an accusation he strongly denies.

Ankara also accuses the movement Gulen leads of being a "terror organisation" although the group insists it is a peaceful organisation promoting moderate Islam.

Those on trial in the western city of Izmir face multiple charges including being a member of the "armed terror group".

Turkey has repeatedly asked the United States to extradite Gulen, who has been living in self-imposed exile there since 1999.

The previous administration of Barack Obama had insisted that a possibly slow legal process should take its course but Ankara is hoping for a more eager response to its extradition request from new President Donald Trump.

Gulen previously went on trial in absentia in January last year over corruption allegations that hit Erdogan in 2013.

The Turkish justice ministry also sent new evidence to Washington for Gulen's return including the indictment for the Izmir case, Anadolu reported on Monday.

The indictment includes witness statements alleging that Gulen was to be presented with the plans for the coup by Adil Oksuz for his approval, the agency added.

Turkish officials have said that theology lecturer Oksuz was the so-called "imam" of the plot and in charge of coordinating between Gulen and the army.

Oksuz was detained in the aftermath of the coup but then released and is now on the run.