Baghdad (AFP) - The scope of the toll the six-week old battle for Mosul has taken on Iraqi forces emerged Thursday, with UN figures showing that around 2,000 had been killed in fighting last month alone.

While high casualty tolls were expected for what has been Iraq's toughest battle against the Islamic State group to date, few figures had been released.

The United Nations' mission in Iraq released monthly casualty figures for November that showed 1,959 members of the Iraqi forces were killed just last month and 450 others wounded.

The UN toll includes members of the army, police 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.

The spike in casualties comes as a major offensive to retake the IS stronghold of Mosul, Iraq's largest military operation in years, enters its seventh week.

Kubis said the growing death toll was largely a result of the jihadists' 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 US-led coalition assisting anti-IS forces in Iraq and Syria admitted Thursday to "inadvertently" killing 54 civilians in both countries between March and October.

"Although the coalition makes extraordinary efforts to strike military targets in a manner that minimizes the risk of civilian casualties, in some cases casualties are unavoidable," the coalition said in a statement.

A July 18 strike that killed 100 IS fighters also killed as many as 24 civilians, the statement added.

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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 on October 17.

- Increase in casualties -

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 explained 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.

The government in Baghdad rarely divulges casualty figures during a military operation.

Officials from the Kurdistan region's peshmerga ministry said more than 1,600 peshmerga fighters were killed since IS took over large parts of Iraq in June 2014.

"Since the beginning of the war against Daesh, which means June 2014, until November 30 (2016), the total number of martyrs is 1,614 and the wounded are 9,515," peshmerga ministry secretary-general Jabar Yawar told AFP.

Burials at the main Shiite cemetery of Najaf, as well as partial figures provided by local officials across the country and the number of obituaries posted on Facebook also pointed to significant losses among the security forces.

After the launch of the offensive in mid-October, tens of thousands of Iraqi forces started closing in on Mosul, retaking towns and villages in Nineveh province.

Iraqi federal forces entered the city from the eastern side and admitted they were met by stiffer than expected resistance.

Military officials and experts had warned before the start of the offensive that the toughest fighting would be on the western side of the city.

The peshmerga were mostly involved in the early phase of the offensive and now hold positions a few miles from Mosul city limits.