GENEVA • About 600,000 people remain in the areas of west Mosul held by the Islamic State in Iraq and Syria (ISIS), including 400,000 who are "trapped" in the Old City under siege-like conditions, the United Nations said yesterday.

"They are desperate for food. They are panicked," Mr Bruno Geddo, who represents the UN refugee agency in Iraq, told reporters in Geneva by phone from a transit centre for displaced people near Mosul.

He said people arriving at the Hammam al-Alil transit centre about 20km south of Iraq's second- largest city described the desperate situation they left behind.

"There is a shortage of fuel, of food, of electricity. People have resorted to burning furniture, old clothes, anything they can use to keep warm at night, because it is still raining heavily and the temperatures at night, in particular, drop significantly," he said.

"It is very, very limited what they can eat," he said, adding that people were surviving primarily on a little bread and water, and many were eating just once a day.

His comments came as Iraqi forces, which launched a massive operation to retake Mosul in October, gain ground from ISIS fighters in the west of the city after taking back the east.

ISIS overran large areas north and west of Baghdad in 2014, but Iraqi forces have since regained much of the territory they lost.

The Iraqis recaptured its eastern sector and launched a major operation to recapture west Mosul - the most-populated urban area still held by ISIS - on Feb 19.

Mr Geddo said around 600,000 people remained in the 60 per cent of west Mosul still under ISIS control, but that number was constantly changing as people fled.

So far, about 153,000 people have fled western Mosul since Feb 19, he said. But many more remain because of shelling and ISIS snipers.

"The worst is yet to come, if I can put it this way," said Mr Geddo.

AGENCE FRANCE-PRESSE, REUTERS