The depths of cruelty the Islamic State of Iraq and Syria (ISIS) has been imparting on its victims knows no bounds as the militants are now selling abducted Iraqi children as sex slaves and even crucifying other youth or burying them alive, the United Nations reported.

According to Reuters, the militant group has been targeting Iraqi boys aged 18 and under either as suicide bombers, bomb makers, informants, or human shields so that their facilities do not get destroyed by United States air strikes.

In a news briefing, committee expert Renate Winter said that the children are even being tortured, especially those belonging to minorities. "The scope of the problem is huge," she said.

Not only does ISIS, also known as the Islamic State of Iraq and the Levant (ISIL) target children from the Yazidi sect or Christian communities, but they have also victimizes Shi'ite and Sunni kids.

"We have had reports of children, especially children who are mentally challenged, who have been used as suicide bombers, most probably without them even understanding," said Winter. "There was a video placed online that showed children at a very young age, approximately eight years of age and younger, to be trained already to become child soldiers."

The U.N. has condemned "the systematic killing of children belonging to religious and ethnic minorities by the so-called ISIL, including several cases of mass executions of boys, as well as reports of beheadings, crucifixions of children and burying children alive."

The militant group has reportedly killed 13 boys earlier via firing squad for simply watching a soccer game.

Because of them, several children have already been killed or badly injured by shielding Iraqi forces during air strikes, while others had died of "dehydration, starvation and heat," the U.N.  revealed.

Not only that, but ISIL has committed "systematic sexual violence," including "the abduction and sexual enslavement of children."

"Children of minorities have been captured in many places, sold in the market place with tags, price tags on them, they have been sold as slaves," Winter shared.

There were 18 independent experts who worked on the U.N. report, and they urged Iraqi authorities to take all necessary measures to "rescue children" who are currently suffering at the hands of ISIL, and to prosecute the people who have harmed thousands of people, including children.