The UN Human Rights Office on Thursday said it has received "credible reports" indicating that more than 231 civilians attempting to flee western Mosul have been killed since May 26, including at least 204 over three days last week alone.
The office said it has been documenting the Islamic State's use of civilians as human shields and its slaughter of those attempting to flee since the start of the Mosul operation, but recent reports indicate "a significant escalation" in such killings.
According to the UN office, on May 26, the IS reportedly shot at civilians trying to flee al-Shifa neighbourhood in western Mosul, killing 27 people, including 14 women and five children.
"Their bodies were reportedly buried two days later by neighbours," the UN office said in a media statement Thursday.
On June 1, the office said, also in al-Shifa, the IS reportedly shot and killed at least 163 civilians, including women, men and children, next to a Pepsi factory.
"Sources reported that the civilians were fleeing armed clashes between ISIL and the Iraqi Security Forces (ISF). The bodies of those who died were reportedly left on the street for several days following the killings," the statement said.
"In addition to those who died, an undetermined number of civilians went missing," it added.
The UN rights office continued that on June 3, the IS reportedly shot and killed at least 41 civilians in the same neighbourhood, as they attempted to flee towards ISF locations.
"Shooting children as they try to run to safety with their families, there are no words of condemnation strong enough for such despicable acts," UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said.
"I call on the Iraqi authorities to ensure that those who are responsible for these horrors are held accountable and brought to justice in line with international human rights laws and standards," he stressed.
According to the UN right office, there are also reports of civilian casualties caused by recent air strikes, including one in Zanjilly, another ISIL-held area of western Mosul, where a strike on May 31 reportedly caused between 50 and 80 civilian deaths.
The office said that its brunch in Iraq is seeking further information about these attacks.