Up to 200,000 more people could flee Mosul as Iraqi forces push into the last districts held by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group, according to the UN.

Nearly 700,000 people have fled Mosul since the start of the campaign to retake the city last October, seeking refuge either with friends and relatives or in camps.

"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 Humanitarian Coordinator for Iraq, said in a statement on Thursday, describing the figures as "alarming".

"The numbers of the people moving are now so large, it’s becoming more and more difficult to ensure civilians receive the assistance and protection they need."

Human Rights Watch said the Iraqi army and other local security officials had forced over 300 displaced families to return to districts of Mosul that are still at risk of attack by ISIL fighters.

"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.

Backed by a US-led coalition, Iraqi forces have dislodged ISIL from all but about 12 square km of the city and are seeking to claim victory before the holy month of Ramadan, which is a little more than a week away.

The ISIL fighters, however, still control the Old City, where they are expected to make their last stand in the densely populated and narrow streets that are impassable for armoured vehicles.

'Very small area'

On Sunday, Brigadier-General Yahya Rasoul said the area controlled by ISIL was no more than nine percent of west Mosul, which is bisected by the River Tigris.

"It's a very small area," he told Reuters news agency. "God willing, this is the final phase."

The Iraqi Counter Terrorism Service stormed the Ureibi and Rifaie districts at dawn on Sunday, according to a statement from the Joint Operations Command.

At the same time, the army's ninth division and the interior ministry's elite Emergency Response Division attacked the ISIL bastion of 17 Tammouz.