A Turkish court has jailed 337 former pilots and other suspects for life over plot to overthrow President Recep Tayyip Erdogan in a failed coup attempt four years ago, a court document obtained by AFP news agency showed on Thursday.

Nearly 500 defendants were accused of carrying out the attempt to overthrow the government on July 15, 2016, from an airbase near the capital Ankara.

More than 250 people were killed in the attempt as rogue soldiers commandeered warplanes, helicopters and tanks in a bid to take control of key state institutions.

The trial was the highest-profile of dozens of court cases targeting thousands of people accused of involvement in the coup attempt, which Ankara blamed on the supporters of the United States-based Muslim preacher and businessman, Fethullah Gulen.

Anadolu and other agencies said at least 25 F-16 pilots were given aggravated life sentences – the most severe punishment in Turkish courts – meaning there is no possibility of parole.

Former air force commander Akin Ozturk and others at the Akinci airbase near Ankara were accused of directing the coup and bombing government buildings, including Parliament, and attempting to kill Erdogan.

Turkey’s then-military chief and now defence minister Hulusi Akar and other commanders were held captive for several hours at the base on the night of the coup.

Four ringleaders, dubbed “civilian imams” over ties to Gulen’s network, were given 79 aggravated life sentences for charges of attempting to assassinate the president, murder, and seeking to overthrow the constitutional order, Anadolu said.

Jazeera’s report said there were 10 civilians in this trial.

“They were present at Akinci airbase where the F-16 that killed the civilians took off from. Prosecutors said these civilians were civil imams of the Gulen movement. They claim they were taking orders from Gulen and passing the order to the military personnel,” she said.

Gulen, 79, who was once an ally of Erdogan and has denied any role in the coup, was one of the six defendants being tried in absentia.

A total of 475 people were on trial, 365 of them in custody.