ISTANBUL — A court in Turkey has sentenced 104 people to life in prison for involvement in the failed military coup of 2016, handing down the heaviest penalties possible in the country.

The defendants were part of a group trial of 280 people, mostly military personnel, accused of participating in an attempt to overthrow President Recep Tayyip Erdogan.

Scuffles broke out at the sentencing on Monday as some of the defendants tried to attack two witnesses who had turned state’s evidence and given details of the plan during the trial, according to Turkish news reports.

The court in Yenisakran, near the coastal city of Izmir in the west of Turkey, convicted 104 of the defendants to “aggravated life,’’ the heaviest sentence possible in Turkey, with very little chance of parole.

An additional 21 people were given 20 years in prison for their part in the attempt to overthrow the president, and 31 others were sentenced to 10 years and six months for “membership of a terrorist organization,’’ the newspaper Hurriyet reported.

The men were on trial for their part in the events of the night of July 15, 2016, when a group of military officers and civilians commandeered tanks and warplanes, firing on protesters and bombing the Parliament building in the capital, Ankara, in an effort to seize power. Erdogan narrowly escaped capture, but 250 people, mostly unarmed civilians, were killed as they faced down tanks on the streets.

Turkey has been holding a series of mass trials for those accused of involvement in the coup, including retired and active military and air force officers, special forces personnel, and cadets who were ordered out from their barracks that night.

The government has accused them of following the orders of the US-based preacher Fethullah Gulen, who is being tried separately in absentia. Turkey has requested his extradition, but US officials have said the Turkish government has yet to provide credible evidence of his involvement.

The latest trial offered some of the strongest evidence to date that the plan was indeed formed by followers of Gulen. Many defendants in this and previous trials denied involvement in the coup attempt or made light of their presence at one of the air bases on the night of the coup attempt.

Among those sentenced were Brigadier Admiral Ibrahim Yildiz and Colonel Hakan Biyik, who had admitted to ties with Gulen’s movement and served as secret witnesses during earlier hearings. Both men received sentences of 16 years and eight months, even after their cooperation with prosecutors was taken into account. Their testimony forms a key part of the extradition request that Turkish prosecutors have submitted to the United States. The Treasury Department is examining Turkey’s extradition request.

Biyik, who went by the code name Cap, told prosecutors that he had been present at planning meetings for the coup in a villa in Ankara, according to Turkish news reports. He identified some of those present and said the meetings, called the Peace at Home Council, were organized by a theology lecturer, Adil Oksuz, who has been accused of playing a leading role in the coup attempt and remains at large.

Yildiz, who went by the code name Raven, has emerged as one of the most important witnesses of preparations for the coup. He also attended the meetings in Ankara and, according to the indictment, testified that at one Oksuz had said he would take the plan to Gulen for his approval and that he had traveled to see Gulen in Pennsylvania three days before the coup attempt, according to Hurriyet.