QAYARA AIR BASE, Iraq (AP) -- The Islamic State group appears to be using tens of thousands of people as "human shields" in and around Mosul, where Iraqi forces are waging a large-scale offensive aimed at retaking the country's second largest city, the U.N. human rights office said Friday.
It has received reports of more than 200 people being killed for refusing to comply with IS orders or previously belonging to Iraqi security forces. It said "credible reports" suggest IS has been forcing tens of thousands from their homes in districts around Mosul.
"ISIL's depraved, cowardly strategy is to attempt to use the presence of civilian hostages to render certain points, areas or military forces immune from military operations, effectively using tens of thousands of women, men and children as human shields," spokeswoman Ravina Shamdasani said in Geneva, using an alternative acronym for the extremist group.
The extremist group has massacred perceived opponents on several occasions, and is widely believed to be rooting out anyone who could potentially rise up against it, focusing on Iraqis with military training or past links to security forces.
The U.N. office said civilians from across the region south of Mosul were being herded into Hamam al-Alil, a militant-held town where the population has more than doubled to 60,000 since the forced displacement began.
There the militants separated former members of the security forces from women and children, and took both groups onward to Mosul, the U.N. agency said. It said 190 former security forces were killed Wednesday at the Ghazlani military base on the southern edge of Mosul, and 42 civilians were killed at another base for refusing to join IS. Another 24 people were reportedly shot dead on Tuesday.
Iraq launched a massive operation on Oct. 17 aimed at retaking Mosul, which fell to IS in a matter of days in the summer of 2014. Iraqi forces are advancing from several directions, but are still well outside the city itself.
The U.S. military, which is providing airstrikes and ground support for the operation, said it tried to disrupt the forced displacement of civilians south of Mosul earlier this week by striking militant vehicles being used in the operation.
U.S. Air Force Brig. Gen. Matthew C. Isler said the U.S.-led coalition conducted "precision strikes" on vehicles that were unoccupied and far away from civilians.
"We were able to do that without harming any civilians and we verified we were able to degrade their planned use of those vehicles," he told The Associated Press. He said the forced displacement was another example of the group's "atrocities."
The AP reported earlier this week that IS militants were going door to door in villages south of Mosul, ordering hundreds of civilians at gunpoint on a forced march north into the city, apparently using them as human shields.
"IS took all of us from our homes at gunpoint and told us they were taking us with them to Mosul," Ahmed Bilal Harish said Wednesday. "They said if you don't come with us you're an unbeliever."
He said he and his family were only able to escape when a volley of airstrikes caused the fighters to scatter during the 25-mile (40-kilometer) trek from their home in the town of Shura to Mosul.
The U.N. and rights groups fear that more than 200,000 civilians could be displaced in the opening weeks of the offensive. Mosul is still home to more than a million people.
IS has built up elaborate defenses on the outskirts of the city, including an extensive tunnel network, and has planted large numbers of explosive booby traps to slow the troops' progress.
Isler said Iraqi forces have retaken 40 villages from IS near Mosul since the operation began. But most of the fighting has taken place in a belt of sparsely-populated farming communities outside the city.
Isler said Iraqi troops were consolidating gains made east and south of the city earlier this week, but insisted "momentum" was still on their side. He said the U.S.-led coalition has stepped up airstrikes against the militants, and is carrying out three times as many as it did during previous campaigns to drive IS from other Iraqi cities.
Iraqi forces are within 4 miles (6 kilometers) from the edge of Mosul on the eastern front, where the elite special forces are leading the charge. But progress has been slower in the south, where Iraqi forces are still 20 miles (35 kilometers) from the city.
The operation to retake Mosul is the largest military offensive launched by Iraq since the 2003 U.S.-led invasion, and involves more than 25,000 troops, Kurdish forces, Sunni tribal fighters and state-sanctioned Shiite militias.
It is expected to take weeks, if not months, to drive the extremist group from its last urban bastion in Iraq.
Moulson reported from Berlin. Associated Press writer Joseph Krauss in Baghdad contributed to this report.