A UN report focused on a range of violations committed against civilians, particularly by the Islamic State, though it also said Iraqi forces and allied fighters had not taken precautions to protect civilians from violence.

"(This)...may also amount to war crimes," the report found.

At least 5,576 Iraqi civilians have been killed this year in violence, the U.N. said in the most detailed account yet of the impact of months of unrest culminating in advances by Sunni militants led by the al Qaeda offshoot Islamic State, formerly known as ISIL, across the north.

"ISIL and associated armed groups have also continued to... perpetrate targeted assassinations (community, political, and religious leaders, government employees, education professionals, health workers, etc.), sexual assault, rape and other forms of sexual violence against women and girls, forced recruitment of children, kidnappings, executions, robberies."

The report also accused them of wanton destruction and plundering of places of worship and of cultural or historical significance.

"Credible information on recruitment and use of children as soldiers was also received," the report noted.

"Every day we receive accounts of a terrible litany of human rights violations being committed in Iraq against ordinary Iraqi children, women and men, who have been deprived of their security, their livelihoods, their homes, education, healthcare and other basic services," U.N. High Commissioner for Human Rights Navi Pillay said.

The report also details violations committed by government forces and affiliated groups, citing "summary executions/extrajudicial killings of prisoners and detainees", which it said may constitute a war crime.

The Iraqi Interior Ministry said this week that an investigation had revealed the Islamic State had taken 510 Shi’ite prisoners from a prison in Mosul to an agricultural area and executed them - killing all but 17 who managed to flee.

The ministry said the its report was based on testimony of one of the prisoners who fled.

GOVERNMENT HAMSTRUNG

Of the 2,400 people killed in June, 1,531 were civilians, the U.N. said earlier this month.

The report called on the government to investigate serious violations and to hold the perpetrators to account.

But the capacity of the Shi'ite-led caretaker government to do so in the face of a Sunni uprising that threatens to fracture the country on sectarian and ethnic lines may be limited.

Iraqi politicians have yet to complete the formation of a new government more than three months after parliamentary elections. Prime Minister Nuri al-Maliki faces pressure from Sunnis, Kurds and some Shi'ites to step aside after two terms in office in which his critics say he marginalized opponents.

The bruised Iraqi army has leaned heavily on Shi'ite militia and volunteers in its battle against the Sunni insurgency. A Shi'ite lawmaker said militia fighters carried out "a lot of assassinations and killings" when first deployed last month, although he said the situation had improved subsequently.

The U.N. noted that the "deteriorating security situation" had limited its ability to directly monitor and verify incidents. More than 1.2 million people had been displaced this year, according to the report.

(Reporting By Maggie Fick; editing by Ralph Boulton)