Iraq’s government asked the UN’s top human rights body on Monday to investigate alleged crimes against civilians committed by the Islamic State group in its rampage across northeastern Syria and northern and western Iraq. The move came as a UN report found that at least 1,420 people were killed last month amid raging battles between the Iraqi army and jihadists.

Diplomats weighed the request at a daylong special session of the 47-nation Human Rights Council on Iraq and the extremist group. A draft resolution put forward by Iraq would set up a UN fact-finding mission to investigate alleged abuses by the group.

Such a mission would be carried out by UN staff, unlike the five independent commissions with outside experts appointed to investigate alleged crimes in the Central African Republic, Eritrea, Gaza, Sri Lanka and Syria.

The Geneva-based rights council created all but one of them; the Security Council, the UN’s most powerful arm, authorized the one on Central African Republic.

The session was focused on the threat posed by the Islamic State group, which has seized cities, towns and vast tracts of land and carried out a number of massacres and beheadings.

Diplomats convened after the US launched a series of airstrikes to prevent the group from advancing on the Kurdish regional capital of Irbil and to help protect members of the Yazidi minority who were stranded in Iraq’s northwest.

The US also launched airstrikes near Iraq’s Mosul Dam, the country’s largest, allowing Iraqi and Kurdish forces to retake the facility from the Islamic State fighters.

In Geneva, UN officials expressed grave concern Monday at the reported atrocities in Iraq, including executing detainees and shelling civilian areas.

“Systematic and intentional attacks on civilians may constitute war crimes and crimes against humanity for individuals,” Flavia Pansieri, the UN deputy high commissioner for human rights, said of both sides fighting in Iraq. “The reports we have received reveal acts of inhumanity on an unimaginable scale.”

An Iraqi militia fighter from Shiite cleric Moqtada al-Sadr's Saraya al-Salam (Peace Brigade), fires a mortar during heavy clashes with Islamic State (IS) fighters in Tuz Khurmatu in Salaheddin province about 88 kilometres (55 miles) south of Kirkuk on August 31, 2014.  (photo credit: AFP/ JM Lopez)

An Iraqi militia fighter from Shiite cleric Moqtada al-Sadr’s Saraya al-Salam (Peace Brigade), fires a mortar during heavy clashes with Islamic State (IS) fighters in Tuz Khurmatu in Salaheddin province about 88 kilometres (55 miles) south of Kirkuk on August 31, 2014. (photo credit: AFP/ JM Lopez)

At least 1,370 people were wounded during August, the UN Iraq mission said in a statement.

It said the figures did not include Anbar province, west of Baghdad, and that there were difficulties in verifying incidents in areas where there was fighting or which were outside government control.

Militants led by the Islamic State overran chunks of five provinces in June, sweeping security forces aside.

After a period of largely static battle lines, the militants launched a renewed offensive in the north in early August, driving Kurdish forces back toward their regional capital anddisplacing hundreds of thousands of people.

Kurdish fighters with US air support have managed to claw back some of the lost ground in the north, and there has also been heavy fighting northeast of Baghdad.