The Iraqi forces took control of eastern Mosul in January after 100 days of fighting, and launched the battle in the west on February 19.
This comes as the Iraqi army and security forces continued to close in on Western Mosul, the final stronghold of ISIS in Iraq's second largest city.
The militants are now surrounded in the northwestern quarter including the historic Old City, using booby traps, sniper and mortar fire against the assailants.
"The sheer volume of civilians still fleeing Mosul city is staggering", said Lise Grande, humanitarian coordinator for Iraq.
According to the top USA commander in Iraq, the battle for Western Mosul is the most brutal urban combat since World War II.
Iraq's army has built a new pontoon bridge over the Tigris river south of Mosul, after flooding blocked all crossing points, to create an escape route for families fleeing fighting between government forces and Islamic State.
Earlier this year, Al Qaeda's leader repeated criticism of the Islamic State's violent attacks, such as beheadings of civilians.
The UN Refugee Agency (UNHCR) has opened a new camp in Iraq's Hammam al-Alil to house thousands of newly-displaced people fleeing the fighting in western Mosul.
Since the start of military operations to retake Mosul six months ago, almost half a million people have been displaced from their homes.
The UN estimates that as many as 500,000 people remain in ISIL-controlled districts in western Mosul, including 400,000 in the densely populated old city. "Families. tell us that they are being shot at as they are escaping". "There are discussions and dialogue between messengers representing ISIS leader Abu Bakr al-Baghdadi and representing al-Qaeda leader Ayman al-Zawahiri".
IS had become an offshoot of al Qaeda in Iraq by 2004, but IS later broke off from the group and became its rival.
This month it was reported the two terror groups had already formed a partnership in Libya amid mounting pressure on the jihadi movements and a leaked memo suggested they could be working together as one organisation by 2021.
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