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BAGHDAD (Reuters) - More than 5 million children are in urgent need of aid in Iraq, the United Nations said on Thursday, describing the war on Islamic State as “one of the most brutal” in modern history.

“Across Iraq, children continue to witness sheer horror and unimaginable violence,” the United Nations Children Fund (UNICEF) said in a statement.

“They have been killed, injured, abducted and forced to shoot and kill in one of the most brutal wars in recent history.”

In Mosul, children are being deliberately targeted and killed by Islamic State militants to punish families and deter them from fleeing, it said.

International organizations estimate that more than 100,000 civilians, of whom half are children, are trapped in extremely dangerous conditions in the Old City center, the last district still under the militants’ control in Mosul.

More than 1,000 children have been killed and more than 1,100 wounded or maimed since 2014, when the ultra-hardline militants seized large swathes of Iraq, it said. Over 4,650 children have become separated from their families.

The militants have lost most of the Iraqi cities they came to control, after a series of U.S.-backed offensives that began in 2015. They are also close to losing all of Mosul, the northern city which served as their de facto capital.