BENGHAZI, Libya — Libya’s Missing Persons Authority announced Sunday the discovery of 42 bodies buried in a mass grave in the central coastal city of Sirte, a former stronghold of the ousted Islamic State group.

In a statement, the authority’s spokesperson said the 42 bodies had been exhumed from a school site in the city following a “tip off” from an investigation conducted with captured Islamic State fighters.

Sirte, the birthplace of former longtime dictator Moammar Gadhafi, fell under Islamic State control between 2015 and 2016, as the extremist group sought to profit from the chaos that engulfed the oil-rich nation since the fallout of the 2011 revolution.

The Islamist group were eventually expelled from the city in December 2016 by forces fighting for the former U.N.-backed Government of National Accord. Hundreds of alleged former Islamic State fighters remain incarcerated in Libyan prisons, many of whom are awaiting trial.

The spokesman for the Missing Persons Authority, Abdulaziz El Mabrouk, said all 42 bodies had since been transferred to a nearby hospital and that samples of their blood, teeth and bones were collected to identify the missing victims. A further 11 corpses were found near the same site in May, he added. No information was provided on the cause of death for any of the bodies.

Several mass graves have been uncovered across Libya in recent years. In December 2018, the bodies of more than 30 men were discovered near Sirte, believed to be the corpses of a group of Ethiopian Christians Islamic State fighters executed in a video the group published years earlier. In the western town of Tarhuna, hundreds of corpses have been uncovered across several graves after militia fighters loyal to Libyan military leader Gen. Khalifa Hifter retreated from the area in June 2020.

Libya was plunged into turmoil after a NATO-backed uprising toppled and killed Gadhafi in 2011. For years the country has been split between rival administrations, each backed by rogue militias and foreign governments. The past months have seen an uptick in deadly militia clashes.

In Tripoli, Prime Minister Abdul Hamid Dbeibah has refused to step down after Libya failed to hold elections last year. His rival, Prime Minister Fathy Bashagha, operates from the eastern city of Benghazi after failed efforts to install his government in the capital.