The remains of hundreds of mainly Shiite inmates killed by Islamic State militants when they overran a prison in northern Iraq more than two years ago have been unearthed by forces retaking the area from the group, a spokesman said.

An Iraqi Shiite paramilitary group made the discovery after driving the militants from the Badush area where the prison is located, as part of a wider U.S.-backed campaign to dislodge Islamic State from the city of Mosul.

As an array of forces dismantle Islamic State's self-proclaimed caliphate across Iraq and Syria, more evidence is emerging of the war crimes committed by the Sunni Islamist militants, who targeted Shiite Muslims and religious minorities as well as opponents from their own sect.