An international rights group says Islamic State militants carried out a mass killing of hundreds of Iraqi prison inmates when they seized the country’s second-largest city of Mosul in June.

Human Rights Watch said Thursday that some 600 male Shiite inmates from Badoosh prison outside Mosul were forced to kneel along the edge of a nearby ravine and shot with automatic weapons.

The New York-based watchdog said in a statement that the Shiite prisoners were separated from several hundred Sunnis a small number of Christians who were later set free. The statement was based on interviews with survivors. […]