IS group fighters may be preparing to use civilians as human shields, or simply kill them, rather than let them be liberated in an Iraqi offensive to retake Mosul, the UN said Friday.
Elite Iraqi troops have been closing in on Mosul, the last jihadist bastion in Iraq, in a long-anticipated offensive.
United Nations human rights chief Zeid Ra'ad Al Hussein said his office had reports that civilians were being held close to IS fighter positions in Mosul, possibly as a buffer against advancing Iraqi forces.
"There is a grave danger that ISIL fighters will not only use such vulnerable people as human shields but may opt to kill them rather than see them liberated," Zeid said in a statement, using another acronym for IS.
Separately, Zeid said his office had reports that the jihadists forced an estimated 200 families to walk from the nearby Samalia village to Mosul last week.
Another 350 families were forced to Mosul from Najafia, according to the rights office.
Those forced displacements were consistent with IS's "apparent policy of preventing civilians from escaping to areas controlled by the Iraqi security forces," Zeid added.
The UN has voiced fears that a million people still trapped inside Mosul could be forced to flee the fighting, sparking a humanitarian emergency.
Speaking to reporters in Geneva by phone, the UN's humanitarian chief in Baghdad, Lise Grande, said the "working scenario" foresees 200,000 people fleeing Mosul, but she cautioned that the numbers could be higher depending on how the military campaign develops.
So far, just 3,900 people have been displaced from the northern city, UN refugee agency spokesman Adrian Edwards said.
He added that UNHCR was working to build up camps and emergency settlements in the area, as humanitarian agencies try to expand their capacity to help civilians as the fighting intensifies.
Aside from caring for those who manage to flee, Zeid stressed that Iraqi military planning for the US-backed offensive needs to prioritise civilian protection, especially with some of the combat expected to take place in confined urban settings.
"We know ISIL has no regard for human life, which is why it is incumbent upon the Iraqi government to do its utmost to protect civilians," he said.