Islamic State fighters executed at least 741 Iraqi civilians in Mosul, including women and children who had tried to flee, during the nine-month battle by government forces to retake the northern Iraq city from the militant group, the United Nations said Thursday.

In a 53-page report detailing atrocities in Mosul that amount to “international crimes,” the United Nations said the executed civilians were among at least 2,521 who were killed during the battle for the city, mostly from Islamic State attacks, including indiscriminate shelling and the use of improvised bombs and — increasingly — explosive-laden drones.

The report said the militants also carried out mass abductions of civilians, used thousands of civilians as shields in combat with Iraqi soldiers, and forcibly recruited boys as young as nine from families then deployed them as “Cubs of the Caliphate” wearing explosive belts.

The report, produced by the United Nations Assistance Mission for Iraq and the Office of the High Commissioner for Human Rights, could be used for war-crimes prosecutions.