Human Rights Watch (HRW) has claimed that militants from the Islamic State (IS) group executed 600 male Shi'ite prisoners at the Badoush prison outside Mosul in June.
The 600 men killed by IS gunmen were Shi'ite Muslims, HRW said.
After capturing the prison on June 10, IS militants herded the 1,500 inmates onto trucks and drove them into the desert, where they separated out the Sunni Muslims and Christians from the Shi'ite prisoners, according to accounts by eyewitnesses who survived the mass killing.
The Shi'ite prisoners were forced to stand in a line along a ravine, after which IS gunmen shot them with a machine gun, one survivor told HRW.
The eyewitnesses said that up to 40 prisoners survived by pretending to be dead or because they were shielded by bodies of other prisoners.
"A bullet hit my head and I fell to the ground, and that’s when I felt another bullet hit my arm. I was unconscious for about five minutes. One person was shot in the head, in the forehead. It [the bullet] went out the other side, and he fell on top of me," one survivor told HRW.
A Sunni prisoner who was among those taken from the prison by IS said that the militants later took the Sunni and Christian inmates to another desert location. IS then separated out as many as 100 men from the group, claiming they were Shi'a masquerading as Sunnis. The rest of the prisoners were taken back to Mosul three days later, where they were released.
IS considers Shi'ite Muslims to be apostates.
There have been other reports of IS militants singling out Shi'a for executions during their takeover of parts of Iraq. In June, residents of four farming villages south of Kirkuk reported that IS gunmen had massacred local Shi'ite Turkmen.
IS militants also carried out a mass killing of as many as 190 captured Iraqi soldiers near Tikrit in June.
-- Joanna Paraszczuk