Islamic fighters in Iraq have killed hundreds of children including in summary executions and used some as suicide bombers, the top UN envoy on children and armed conflict said Monday.
"Up to 700 children have been killed or maimed in Iraq since the beginning of the year, including in summary executions," Leila Zerrougui told the UN Security Council.
Zerrougui said Islamic State (IS) fighters were recruiting boys as young as 13 to carry weapons, guard strategic locations and arrest civilians.
"Other children are used as suicide bombers," she added.
Militias allied to the Iraqi government are also using children to combat the jihadists and "numerous children" detained by the government went missing after militias stormed the prisons in July, she added.
World governments and the United Nations have repeatedly accused Islamic State fighters of atrocities since they overran large swathes of Iraq and Syria in June.
New UN High Commissioner of Human Rights, Zeid Ra'ad Al Hussein, said in Geneva earlier that the Islamic militants were creating a "house of blood" in the zones that they control.
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The accusations came ahead of a UN summit to be hosted by US President Barack Obama on September 25 on the threat of foreign fighters seen as fueling the fighting in Iraq and Syria.
The UN Security Council last month adopted a resolution that seeks to choke off funding and the flow of foreign fighters to the Islamists, and warns that the string of atrocities may constitute crimes against humanity.
The council on Monday was holding a debate on child soldiers, with the focus also on Libya, Afghanistan, Central African Republic, Mali and South Sudan where children are being recruited as soldiers.
In the Central African Republic, about 8,000 children have been enlisted to fight in various armed groups, UN peacekeeping chief Herve Ladsous told the council.
The top UN body heard an appeal for reintegration from US actor Forest Whitaker, a goodwill ambassador for UNESCO, whose foundation is active in South Sudan.
"How alone these children must feel when they return from the battlefield to a world they do not recognize," said Whitaker.
"Unless we are there to meet them with open arms, open homes, and open schools, their wars will never end. And neither will ours."
A "Children, Not Soldiers" campaign was launched at the United Nations earlier this year with the goal of ensuring that no children are serving in government forces by the end of 2016.