Nearly 2,000 soldiers and hundreds of civilians were killed in Iraq in November, the UN said on Thursday, in a "staggering" spike in deaths coinciding with operations to retake the Islamic State-held city of Mosul.

The figure increased threefold from October, when tens of thousands of troops launched an assault to retake the Islamic State (IS) group's last major Iraqi bastion of Mosul.

According to the UN mission in Iraq's monthly tally, 1,959 Iraqi forces were killed last month and at least 450 others wounded.

'The casualty figures are staggering' - Jan Kubis, UN envoy

That figure is just under half the number of American soldiers killed after the US invaded the country in 2003.

The toll includes members of the army, police who are engaged in combat, the Kurdish peshmerga, interior ministry forces and pro-government paramilitaries.

The UN statement also said at least 926 civilians were killed, bringing to 2,885 the number of Iraqis killed in acts of terrorism, violence and armed conflict last month.

"The casualty figures are staggering, with civilians accounting for a significant number of the victims," the top UN envoy in Iraq, Jan Kubis, said.

Kubis said the growing death toll was largely a result of the IS group's ferocious defence of Mosul, the city where they proclaimed their now crumbling "caliphate" in 2014.

"Daesh (IS) has been employing the most vicious tactics, using civilian homes as firing positions as well as abducting and forcibly moving civilians, effectively using them as human shields," he said.

The UN did not provide a regional breakdown of the overall toll but its casualty figures have been going up steadily since the launch of the Mosul offensive.

The number of members of the Iraqi forces killed released by the UN for October was 672.

The highest number of civilian deaths recorded in November was in Nineveh province, of which Mosul is the capital, with 332, the UN figures showed.

The UN said it had few reliable figures for the western province of Anbar, which has seen continued IS-related violence in recent weeks, and suggested that real casualty figures were likely higher.

'It is reasonable to expect that this is going to take weeks if not months' - Dominik Stillhart, Red Cross

Separately, a senior official of the International Committee of the Red Cross told Reuters that it expected the Mosul campaign to last for "weeks if not months".

A growing number of wounded, more than 100 on some days, were emerging from rural areas surrounding the city, said Dominik Stillhart, director of ICRC operations worldwide.

"What we see now on the ground is indeed that the fight in Mosul is not just going to stop anytime soon because the resistance is very strong," he said.

"It is likely that we will see long, drawn-out fighting with very serious suffering of a population that will once again be caught between two frontlines," he said. "It is reasonable to expect that this is going to take weeks if not months."