As Iraqi troops waged fierce battles Friday with ISIS militants in Mosul’s eastern neighborhoods, the United Nations warned it believes the terror group is seizing boys as young as 9 to fight on its behalf.

It has received reports ISIS has been instructing residents of Hammam al-Alil, about 30 kilometers (18.6 miles) south of Mosul, to hand over boys 9 and older since October 17, Ravina Shamdasani, spokeswoman for the UN refugee agency, said at press briefing in Geneva, Switzerland.

She said the boys were apparently being conscripted to fight on behalf of the terror group as it battles to hold on to its Iraqi stronghold in the face of a massive assault by Iraqi-led coalition forces.

Shamdasani said the United Nations continued to receive reports of mass killings by ISIS, including 50 of its own militants Monday at Mosul’s Ghazlani military base for alleged desertion.