Doubts are growing about the authenticity of an edict attributed to the Sunni Islamist group Isis controlling the Iraqi city of Mosul about female genital mutilation (FGM).
A top UN official quoted from a statement saying that Isis wanted all females aged between 11 and 46 in the northern city to undergo the procedure.
Jacqueline Badcock said the decree was of grave concern.
But media analysts say the decree seen on social media may be a fake.
It has typos and language mistakes and is signed by "The Islamic State in Iraq and the Levant", a name the group no longer uses, instead referring to itself as the Islamic State.
Some bloggers suggest that the alleged fatwa, which has been circulated on social media for about two days, may have been aimed at discrediting Isis.
Iraq is facing a radical Isis-led insurgency, with Mosul and other cities in the north-west under militant control.
The ritual cutting of girls' genitals is practised by some African, Middle Eastern and Asian communities in the belief it prepares them for adulthood or marriage.
FGM poses many health risks to women, including severe bleeding, problems urinating, infections, infertility and increased risk of newborn deaths in childbirth.
The UN General Assembly approved a resolution in December 2012 calling for all member states to ban the practice.
Earlier, Ms Badcock warned that the alleged Isis edict could affect nearly four million women and girls in and around the northern Iraqi city of Mosul.
The UN's resident and humanitarian co-ordinator in Iraq said the practice "is something very new for Iraq... and does need to be addressed".
She was talking to reporters via video link from the Kurdish provincial capital, Irbil.
Jenan Moussa, a correspondent for Dubai-based broadcaster Al AAan TV, said in a tweet that her contacts in Mosul had not heard of the edict.
Isis militants seized Mosul, Iraq's second largest city, in June, and have since taken over areas of the north-west and closed in on cities near Baghdad.
The group forced Christians in Mosul out of the city earlier this week and daubed their houses with the Arabic letter N to mark them out as Christians, apparently confiscating their properties, BBC Arab affairs editor Lina Sinjab says.
FGM and child marriage
have undergone FGM
29 countries in Africa and the Middle East practise FGM
33% less chance a girl will be cut today than 30 years ago
But rising birth rate means more girls in total are affected
250m women worldwide were married before age of 15
Ms Badcock said only 20 families from the ancient Christian minority now remain in Mosul, which Isis has taken as the capital of its Islamic state.
Thousands have fled into Kurdish-controlled territory in the north.
Some of the Christians who remained have converted to Islam, while others have opted to stay and pay the "jiyza", the tax imposed by Isis on non-Muslims, the UN official added.
Isis announced last month that it was creating an Islamic caliphate covering the land it holds in Iraq and Syria.
Female genital mutilation
- Includes "the partial or total removal of the female external genitalia or other injury to the female genital organs for non-medical reasons"
- Practised in 29 countries in Africa and some countries in Asia and the Middle East
- An estimated three million girls and women worldwide are at risk each year
- About 130 million victims estimated to be living with the consequences
- It is commonly carried out on young girls, often between infancy and the age of 15
- Often motivated by beliefs about what is considered proper sexual behaviour, to prepare a girl or woman for adulthood and marriage and to ensure "pure femininity"