ISIS confirmed his death in a video montage, in which he is referred to as "the martyr of the battle."
The Iraqi military sources also say that al Nuaimi was formerly a high-ranking intelligence officer in Saddam Hussein`s intelligence services, which CNN cannot independently confirm.
As the battle for the beleaguered northern Iraqi city wears on, the sources say that two Mosul residents were killed when an ISIS mortar attack intended for Iraqi troops hit civilian homes in the Kirkukli neighborhood.
Car bombs, booby traps
As troops battle through the narrow, dense streets of Mosul, witnesses say that ISIS are positioning car bombs among houses in the neighborhoods of al Baker, Aden and al Intisar.
Ongoing clashes in Aden were reported Thursday evening, following several airstrikes which hit ISIS positions in the neighborhood.
Witnesses say that one such device was detonated as Iraqi forces approached, destroying seven houses. It is unclear whether there were casualties.
Also in the city`s east, residents say that ISIS militants were forcing them from their homes, either to booby trap them or to take them over as fighting positions. Militants have also reportedly left barrels full of crude oil at major intersections, ready to be set alight to further hamper Iraqi advances.
Terror campaign continues
ISIS executed seven men, who they had accused of spying for the Iraqi military, in the western area of the city, according to military sources. The men, which were dressed in orange jumpsuits, were the latest victims of an ongoing campaign of terror by the militant group in Mosul.
Jihadists have been killing suspected Iraqi Security Forces (ISF) collaborators since Monday, witnesses say. All the victims have been male, the witnesses say, and have been shot in the head. Many are former Iraqi soldiers and policemen. As many as 75 were killed in an incident ten days ago.
The suspected spies` bodies have been left at intersections throughout the areas of the city that the group still controls.
Some witnesses say dozens of bodies are piling up at some junctions -- stark warnings to residents not to collaborate with the incoming Iraqi forces.
The corpses have been seen in areas on both sides of the city, among them the Zuhur and Karama neighborhoods in the east, and the old city on the west side of the river.
CNN cannot independently confirm the accounts.
In some neighborhoods, residents say, local ISIS commanders have started fleeing, leaving behind trained teenage ISIS combatants to fight Iraqi forces.
The Mosul residents CNN spoke with say they fear the teenage fighters as much, if not more, than other ISIS fighters because they have been brainwashed, have no fear and have a great amount of zealotry after being indoctrinated and trained for two years.
After what was described by witnesses as an airstrike on an ISIS police center in the eastern al Qazah neighborhood, residents ran into the damaged building to recover personal documents previously seized by ISIS.
Among the documents were said to be identification cards, lists of residents` names compiled by ISIS and SIM cards confiscated by ISIS two weeks ago.
Bloody battle
When the long-awaited offensive began October 17, Iraqi Prime Minister Haider al-Abadi vowed victory but warned the effort could take time.
ISIS, an agile enemy, has been preparing its defenses for two years. It takes advantage of the terrain, a network of tunnels and booby-trapped buildings, to great effect.
U.S. military officials estimate there are 3,000 to 5,000 ISIS fighters in Mosul. An additional 1,500 to 2,000 ISIS fighters may be waiting outside the city limits.
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