Some ISIS supporters have denied the claims, branding them '

There was anger last night after it emerged militant group ISIS may have ordered compulsory female genital mutilation (FGM) for all women and girls in a region of Iraq now under its control.

The extremist group has seized large swathes of the troubled country's northern regions and is now said to be imposing its hardline Sharia rules on the population.

The United Nations expressed deep concern yesterday at reports all girls and women in and around city of Mosul are to being forced to undergo FGM procedures.

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ISIS militants have reportedly ordered that women and girls in an area of Iraq under their control undergo FGM

A UN spokesman in Geneva said that they were seeking clarity and trying to establish the facts.

Such a 'fatwa' issued by the Sunni Muslim fighters would potentially affect 4million women and girls, according to UN resident and humanitarian coordinator in Iraq Jacqueline Badcoc.

'We have current reports of imposition of a directive that all female girl children and women up to the age of 49 must be circumcised.

'This is something very new for Iraq, particularly in this area, and is of grave concern and does need to be addressed,' Badcock said.

'This is not the will of Iraqi people, or the women of Iraq in these vulnerable areas covered by the terrorists,' she added.

But doubts emerged on social media about the basis for the report. One document posted on Twitter suggested it may be a year old and have been issued by the Islamic State of Iraq and Levant, the group's previous name.

The hardline group, whose members are pictured in Syria, have been parading through the streets of Iraq with military equipment since seizing large swathes of the country

The owner of one Twitter account, which contains multiple images of the decapitated heads of Syrian soldiers, said the claims were 'a lie'.

Other Internet comments, including from Middle East analysts, questioned whether the order would fit with the cultural traditions of the region.

There was no immediate comment from ISIS, which has led an offensive through northern and western Iraq.

The U.N is said to have 'zero contact' with the miltants, but works through tribal leaders in the affected areas, Badcock said.

She added: 'I can't give you any more details until we have been on the ground to get information.'

The group have even published a report boasting of their achievements, including the number of bombings

FGM, the partial or total removal of external female genitalia, is a tradition practised widely in many African and Muslim countries and often justified as a means of suppressing a woman's sexual desire to prevent 'immoral' behaviour.

Worldwide, more than 130 million girls and women have undergone FGM and more than 700 million women alive today were children when they were married.

The practice of FGM previously occurred only in isolated pockets of Iraq, mainly Kurdistan, according to Badcock.

Mosul city currently has some two million people, more than half of whom are women as there are many female-headed households in the area, she said. Several more million people live in surrounding areas, she added.