Islamic State militants have carried out atrocities on “an unimaginable scale” over several months of fighting in Iraq, a UN official said in an emergency debate Monday. The UN agreed to send a commission to the country to investigate.

The UN Deputy High Commissioner for Human Rights, Flavia Pansieri, who opened the debate in Geneva, said there is “strong evidence” that Islamic State (IS), formerly known as ISIS, groups have carried out numerous atrocities including killings, beheadings, torture, sexual abuse and conversions.

“The reports we have received reveal acts of inhumanity on an unimaginable scale. Systematic and intentional attacks on civilians may constitute war crimes and crimes against humanity. Individuals, including commanders, are responsible for these acts,” she said.

Pansieri added that she was particularly concerned with the persecution of Iraq’s religious minorities including the Shia, Yazidis, Christians and Turkmen.

“These communities have lived side by side, on the same soil, for centuries and in some cases for millennia,” she said, adding that IS has carried out ethnic and religious cleaning.

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The Yazidis have suffered extremely harshly under IS. Many men who refused to convert to Islam were reportedly executed and at least 2,250 Yazidi women and children are being held as hostage, while others are used as sex slaves.

She added that Iraqi police and government forces had also committed acts that amounted to war crimes.

Government allied militias opened fire on a mosque in Khanaquin district north east of Baghdad, killing 73 men and boys and Iraqi police executed a number of detainees in Tal Afar.

Iraqi forces have also shelled towns and carried out airstrikes near Kirkuk, Fallujah, and Salahuddin, which killed and injured dozens of civilians.

The one day UN session was called by Iraq with the support of its allies and agreed to a request by Baghdad to send a team of UN experts to investigate the crimes committed since IS swept through Iraq in June.

Mohammad Shia al-Sudani, Iraq’s Human Rights Minister, told the session that IS was “oozing with barbarity” and threatened the make-up of his country and the entire world, but did not respond to allegations of atrocities carried out by Iraqi troops.

“The land of ancient Babylon is subjected to threats to its very independence, they are attempting to change its demographic and cultural composition,” he said.

ISIS is a "trans-national phenomenon that poses an imminent danger to all countries of the world, it defies all human rights principles and international law,” he added.

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The Sunni Muslim Gulf states as well as the West have all denounced IS, although they bear some of the responsibility for its rapid rise to dominance for indirectly helping to create a situation in Iraq and to a lesser degree Syria, where such an organization could thrive.

“The organization has nothing to do with Islam, even if they carry the name,” said Jamal al-Ghunaim, Kuwait’s ambassador.

Russia, which has also supplied some arms to counter IS, said that the rise of IS could have been avoided.

"ISIS acquired a huge potential: it now controls colossal financial resources that it has seized, is pursuing illegal oil trade and has a considerable arsenal of modern weaponry. All this could have been avoided if the international community had taken measures at the time to remove this cancer at an early stage of its formation," said Moscow's ambassador to the UN in Geneva, Aleksey Borodavkin.

In August at least 1,420 people were killed in Iraq, the UN estimated. A further 1,370 Iraqis sustained injuries while 600,000 people were forced to flee as the IS, which has grabbed large areas of territory since June, pushed into land controlled by Kurdish troops.