Iraqi authorities and aid agencies are already struggling to cope with a surge in displacement since security forces opened a new front against the militants in Mosul this month.
Backed by a U.S.-led coalition, Iraqi forces have dislodged IS from all but about 12 square kilometers (five square miles) of the city and are seeking to claim victory before the holy month of Ramadan in less than two weeks.
The militants, however, still control the Old City, where they are expected to make their last stand in the densely populated, narrow streets that are impassible for armored vehicles.
Military commanders say the aim is to raise the Iraqi flag over the Old City's Nuri mosque, from which IS leader Abu Bakr al-Baghdadi proclaimed a caliphate, so the battle can be declared won even if pockets of resistance remain.
'As military operations intensify and move closer to Mosul's Old City area, we expect that up to 200,000 more people will flee,' Lise Grande, the U.N.'s humanitarian coordinator for Iraq, said in a statement, describing the figures as 'alarming.'
'The numbers of people who are moving are now so large, it's becoming more and more difficult to ensure civilians receive the assistance and protection they need,' she added.
FILE - A humvee of the Iraqi Federal Police drives through an abandoned street in western Mosul, Iraq, May 2, 2017.
Complications for Iraqi advance
The displacement is also complicating the advance of Iraqi forces, according to Brigadier General Ali al-Sharifi of the Federal Police, which are fighting in the 17 Tammouz district.
'We didn't expect such a flux of thousands of families fleeing toward our forces,' al-Sharifi said. 'We slowed clashes to give them safe routes, and we had to prepare hundreds of trucks to evacuate them. It's not an easy situation.'
Among those freed from IS Thursday were two girls from the Yazidi minority who had been held captive since the militants overran their villages nearly three years ago, Federal Police chief Lieutenant General Raed Shaker Jawdat said in a statement.
Seven months since the start of the Mosul campaign, nearly 700,000 people have fled Mosul, seeking refuge either with friends and relatives or in camps.
Human Rights Watch said Thursday that the Iraqi army and other local security forces had forced over 300 displaced families to return to western districts of Mosul that are still at risk of IS attack.
'These families should not be forcibly returned to unsafe areas and areas that lack adequate water, food, electricity or health facilities,' said Lama Fakih, deputy Middle East director at Human Rights Watch.