The exodus of civilians from Mosul has reached an unprecedented level, leaving aid agencies struggling to cope, amid further gains by Iraq's joint forces in the battle to retake the city.

"The numbers of people fleeing their homes in western Mosul are overwhelming," Lise Grande, the UN humanitarian co-ordinator in Iraq said on Thursday (May 18th).

"We are talking about very large numbers of families who are leaving everything behind," she said. "They are fleeing under very difficult circumstances. Many are food insecure and have not had access to safe drinking water and medicines for weeks or months."

Meanwhile, Iraqi forces continue to engage "Islamic State of Iraq and Syria" (ISIS) militants in street-to-street fighting inside the western part of Mosul.

Iraqi forces have retaken limited areas of al-Najjar neighbourhood and rolled into Bab Sinjar, Joint Operations Command spokesman Brig. Gen. Yahya Rasul told Diyaruna on Thursday.

"They also have retaken the intersection of Khawla Bint al-Azwar School," he said.

"Thirty-one terrorists were killed in the battles, and others, including snipers believed to be non-Iraqis, have been encircled," he said.

"We are now working on eliminating them or forcing them to surrender," he added.