Twenty-nine Turkish police officers went on trial on Tuesday accused of failing to defend President Recep Tayyip Erdogan during the military's failed coup in July, the first such case in Istanbulinfo-icon.

The hearings follow a massive crackdown on alleged putschists -- 41,000 are under arrest in a national state of emergency and the trials are set to be the most far-reaching legal process in the country's historyinfo-icon.

Five months after the coup attempt, small-scale cases involving suspects have already begun in the provinces and on Monday 60 people went on trial in the southwestern city of Denizli.

But the trial in Istanbul -- in a gigantic courthouse outside the Silivri prison in the city -- is the most significant to date. The government says 248 people were killed by the coup plotters.

The accused are charged with seeking to overthrow the government as well as allegedly being members of the group led by USinfo-icon-based preacher Fethullah Gulen who the authorities accuse of leading the plot.

Gulen, who Turkeyinfo-icon wants to see extradited from the United Statesinfo-icon, vehemently denies the charges.

Of the 29 police on trial in Istanbul, 24 are under arrest, one on the run and the rest on bail.

Special forces in camouflage gear stood guard outside the courthouse and snipers were posted on the balconies of nearby minarets.

The names of the accused and the indictment were read out, the state-run Anadolu news agency said. Arguments for the defence are expected to follow with the initial hearings expected to last until Friday. If convicted, 21 suspects each face three life sentences on charges of staging a coup.