The office also has received reports of over 200 people being killed for refusing to comply with IS orders or for previously belonging to Iraqi security forces, spokeswoman Ravina Shamdasani said in Geneva.
"Credible reports" suggest that IS has been forcing tens of thousands from their homes in districts around Mosul since a massive operation to drive the militants from the city began last week, Shamdasani said, with other civilians being relocated within the city itself.
The militants apparently are collecting people from the outskirts of Mosul and pushing them into the city "to be able to keep them close to military installations, close to their offices," she said.
"Many of those who refused to comply were shot on the spot, and even among those who did comply, many of them -- including 190 former ISF officers and 42 other civilians -- were shot dead," Shamdasani added.
Those killings reportedly happened on Wednesday, and another 24 former officers with the Iraqi security forces were reportedly killed on Tuesday.
Shamdasani said that the reports "have been corroborated to the extent possible.