Iraqi paramilitary forces announced on Saturday that they had discovered a mass grave at Badush prison near Mosul containing the remains of hundreds of people killed by Daesh.
Daesh killed up to 600 inmates after seizing Badush in 2014, according to Human Rights Watch (HRW).
Daesh forced them to kneel along a nearby ravine and then shot them with assault rifles. Most of those murdered were said to have been members of Iraq's Shia Muslim majority.
Hashd al Shaabi found "a large mass grave containing the remains of around 500 civilian prisoners in [Badush] prison who were executed by [Daesh] gangs after they controlled the prison during their occupation of Mosul," the military said.
The Iraqi military said that forces from the Hashd al Shaabi — an umbrella group of pro-government forces that are dominated by Iran-backed Shia militias — were among the units that recaptured the prison from the terrorist group.
Daesh abuses at the jail did not end with the murdering its inmates. Iraqi lawmaker Vian Dakhil said in 2014 that the group was holding more than 500 Yazidi women at Badush.
The remains of some 500 people executed by Daesh were found at Badush prison near Mosul. pic.twitter.com/8dPq7UIxXe
— TRT World (@trtworld) March 11, 2017
The Badush site is not the first mass grave to be found during the Mosul campaign, in which Iraqi forces recaptured areas around Mosul before battling Daesh inside it.
Iraqi forces found one in the Hamam al Alil area south of Mosul in November that an official said appeared to hold the remains of at least 25 bodies.
And earlier this year, Iraqi forces retook an area containing a sinkhole known as the Khasfah, which could be the largest mass grave of the war with Daesh.
Local residents said that Daesh used it as an "execution site" and a mass grave where they would dispose of victims.
HRW examined satellite imagery that suggested the sinkhole was filling up, and local residents said that Daesh had piled rusted car parts and shipping containers into it, before bulldozing earth on top.
Daesh overran large areas north and west of Baghdad in 2014, but Iraqi forces backed by US-led air strikes have since regained most of the territory they lost.