More than 220 suspects, including over two dozen former Turkish generals, have gone on trial accused of being among the ringleaders of the attempted coup last year aimed at ousting President Recep Tayyip Erdogan.

Protesters outside Turkey's largest courtroom in the Sincan district of Ankara called on Monday for the death penalty for the accused and flung rope nooses at the defendants as they were paraded into court handcuffed and held by the security forces.

"We want the death penalty, we don't want them to be fed and housed here. We want these traitors to be buried without any flag," said protester Cengiz Ozturk.

Turkey abolished the death penalty as part of its drive to join the European Union but Erdogan has on occasion indicated it could be reimposed to deal with the coup plotters.

There was heavy security in place on Monday, with a drone flying overhead and armoured security vehicles on site as well as snipers on the roof.

Hearings at the trial, one of the largest of several coup-related trials taking place across Turkey, are expected to last until June 16.

Turkey blames the attempted July 15 putsch on the US-based Muslim cleric Fethullah Gulen, a claim he strongly denies, and has launched a relentless purge under a state of emergency against those deemed to have backed the plot.

Gulen is among 12 of the 221 suspects in the current trial who remain at large, with the remainder appearing in court for the first time inside a prison complex in Sincan.

READ MORE: Turkey's failed coup attempt - All you need to know

Twenty-six generals are among those charged, including former air force chief Akin Ozturk and Mehmet Disli, the brother of senior ruling party politician Saban Disli.

Also on trial is Colonel Ali Yazici, Erdogan's former military aide, and Lieutenant-Colonel Levent Turkkan, who was the aide of Chief of Staff General Hulusi Akar.

The most prominent figure among the suspects, Ozturk was dressed crisply in a black sweater and held a blue file as he was led into the court.

His appearance contrasted with the last-known image of him, which showed him bearing injuries including a bandaged ear after his capture two days after the coup bid.

Almost 40 of those on trial are accused of being part of the "Peace At Home Council", the committee established by the suspected coup plotters to replace the government if the putsch had succeeded.

The charges against them include "violating the constitution", "using coercion and violence in an attempt to overthrow" the parliament and the Turkish government, "martyring 250 citizens" and "attempting to kill 2,735 citizens", Hurriyet daily reported on Sunday.

The attempted putsch left 248 people dead, according to the Turkish presidency, not including 24 coup-plotters killed on the night.