Iraq on Sunday executed 36 men convicted of taking part in the Islamic State of Iraq an Syria (ISISmassacre of hundreds of soldiers in 2014, officials said.

The men were hanged at the Nasiriyah prison in southern Iraq, according to provincial Gov. Yahya al-Nasiri.  A Justice Ministry official, who spoke on condition of anonymity because he was not authorized to brief reporters, confirmed the executions.

ISIS captured an estimated 1,700 soldiers after seizingSaddam Hussein’s hometown of Tikrit in 2014. The soldiers were trying to flee from nearby Camp Speicher, a former U.S. base just outside the northern city. Shortly after taking Tikrit, ISIS posted graphic images of gunmen shooting the men dead after forcing them to lie face-down in a shallow ditch.

The Speicher massacre sparked outrage across Iraq and partially fueled the mobilization of Shiite militias in the fight against ISIS, a Sunni extremist group. The militias now rival the power of Iraq’s conventional armed forces.