(Adds Yazidi women recovered, federal police statement)
By Isabel Coles and Ahmed Rasheed
ERBIL/BAGHDAD, Iraq, May 18 (Reuters) - The United Nations said on Thursday up to 200,000 more people might flee Mosul as Iraqi forces push into the last districts held by Islamic State militants.
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 earlier this month.
Backed by a U.S.-led coalition, Iraqi forces have dislodged Islamic State from all but about 12 square km (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 Islamic State 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 UN'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."
The displacement is also complicating the advance of Iraqi forces, according to Brigadier General Ali al-Sharifi of the Federal Police forces, which are fighting in the 17 Tammouz district.
"We didn't expect such a flux of thousands of families fleeing towards our forces. 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 Islamic State on 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 on Thursday 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 attack by Islamic State.
"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. (Reporting by Isabel Coles and Ahmed Rasheed; Editing by Lary King)