Battle hardened ISIS fighters are hanging tough inside the city of Mosul as they desperately cling on to their last remaining stronghold in Iraq.

Iraqi troops called on heavy coalition air strikes over the weekend to try and aid their push inside the strategic city that has been held by the extremists since 2014.

Militants are dug in among more than a million civilians as a defence tactic to hamper air strikes. They are moving around the city through tunnels, driving suicide car bombs into advancing troops and hitting them with sniper and mortar fire.

Footage purportedly taken west of Mosul shows Iraqi fighters trying to stop an advancing ISIS Humvee, laden with explosives.

Soldiers spray the death machine with automatic gunfire but are unable to stop it exploding in a giant fireball next to vehicles and homes.

A second video , also published by Syrian propaganda organisation Stahlgewitter Syrien, documents through a drone the surreal surrender of an alleged ISIS fighter.

The hovering drone captures the ISIS fighter stripping himself of clothes and weapons, before trudging across yellow sands to a waiting unit of Iraqi fighters.

A 100,000-strong alliance of Iraqi forces, with air and ground support from a US-led coalition, have nearly surrounded Mosul but so far only breached the jihadists' defences from the eastern side, establishing a small foothold inside the city.

The Iraqi authorities do not release comprehensive casualty statistics, but the U.N. figures probably represent just a fraction of the total as they capture only the most severe cases that cannot be treated on site, and do not include fatalities.

"We are very worried that more and more civilians will be hurt and victimised as the campaign intensifies," said Grande. "Civilians are not being caught in cross-fire, they are being targeted."

The desperate plight of civilians is clear to see in video of food trucks arriving in parts of the city freed from ISIS.

Men, women and children swarmed trucks as boxes of aid were handed out.

People said they had suffered from lack of food and water while living under the control of Islamic State.

"We suffer from mortars and sniper fire. We also suffer from the absence of electricity. We cannot operate generators because we do not have gasoline," said Abu Ahmed, a resident of Zahraa neighbourhood.

"The delivery of water depends on the availability of electricity, therefore, when we do not have electricity, we will not have water. We have to take water

from wells. There is no fuel either."