Turkey has opened its biggest trial yet of people suspected of being involved in plotting a coup that failed in July last year.

A total of 270 suspects are being tried in Izmir for trying to oust President Recep Tayyip Erdogan, including several high-ranking military officers.

Among those going on trial is the plot's alleged mastermind Fethullah Gulen, who is currently in the US in exile, and a former NATO Land Commander in Chief.

Ankara accuses the movement led by Gulen, an Islamic preacher, of being a "terror organisation" but the group insists it is a peaceful organisation promoting moderate Islam.

Former US president Barack Obama told Turkey the extradition of Gulen would be a long and slow process, but Ankara is hoping the new administration under Donald Trump may help speed it up.


Image: Fethullah Gulen is in exile in the US

Prosecutors say they have witness statements alleging that Gulen was to be given the plans for the coup for his approval by co-plotter by Adil Oksuz.

They say theology lecturer Oksuz was the so-called "imam" of the plot and in charge of co-ordinating between Gulen and the army.

Oksuz was held after the coup, but then released and is now on the run.

Other suspects are charged with trying to prevent parliament performing its duty and attempting to remove the constitutional order.

Hurriyet newspaper reported that all will face life sentences if they are convicted in a trial expected to take two months.

About 43,000 people remain under arrest following a large-scale crackdown that came during a state of emergency as declared after the coup.