Updated

A top U.N. official said Monday she was overwhelmed by the suffering of children during a recent visit to Syria and warned officials and rebel commanders alike that they risk prosecution as war criminals for atrocities against minors.

Leila Zerrougui, the Special Representative of the Secretary-General for Children and Armed Conflict, said she met parents whose children were killed in bombings, children who saw siblings die in front of them and teenagers who had fought with armed opposition groups. She visited both Syria and neighboring countries that are hosting hundreds of thousands of refugees from the civil war.

Around 7,000 children under the age of 15 have been killed during Syria's more than two-year-old conflict. Half of the 1.7 million Syrian refugees are children, and inside the war-ravaged country, more than 3 million children are in desperate need of humanitarian aid.

A recent U.N. report placed the main rebel umbrella group, the Free Syrian Army, on its "list of shame" for recruiting child soldiers. Syrian government forces were added to the list for detaining minors and often torturing and sexually assaulting them.

Zerrougui said one of her main goals during her visit was to make clear to both sides that the United Nations is keeping track of atrocities and that perpetrators would not escape persecution.

"You can't imagine when you go to a hospital and you see a child without a leg ... and then you see the brother lying on the bed who lost a kidney, who lost a pancreas and the mother is sitting near. Those are the realities that you see," Zerrougui said at a news conference.

"One day Syria will come to peace, and those committing the atrocities will have to face, I hope, justice," she said.

Zerrougui said she met teenagers who fought with armed opposition groups. She said the U.N. is verifying reports that armed groups were forcing some families to send their teenage children to war in exchange for protection. But many minors, she said, were following relatives to war, making it important to convince commanders not to let such children join their ranks.

She said it was a difficult message to get across: Most commanders on the ground denied recruiting children and insisted everyone in their ranks was at least 18. That denial came even though the leadership of the Free Syrian Army has acknowledged the problem and sent Zerrougui a letter asking for guidance on how to get off the "list of shame."

The government of President Bashar Assad recently passed a law prohibiting child soldier recruitment. But Zerrougui said she emphasized to Syrian government officials that if they consider child soldiers victims, authorities must stop detaining them as criminal suspects. She said Syrian authorities continue detaining children on security charges or because their families are suspects of sympathizing with the opposition.

Zerrougui said she feels a political solution is the only way out for Syria, but she was struck by the polarization that is making compromise more difficult.

Of the four government ministers she met, Zerrougui said, "three had lost a sister, a son or a brother, killed by the other side. This is the reality of Syrian families. This creates a lot of anger and polarization."

The Syrian regime feels "it has no other option but to win this war," she said.