The Islamic State of Iraq and Syria group is committing war crimes and crimes against humanity on a large scale in areas under its control, a U.N. panel investigating war crimes in Syria said Friday.

The U.N. Commission of Inquiry on Syria presented a horrific picture of what life is like in areas controlled by ISIS militants in its first report on the group.

Based on more than 300 interviews with people who have fled areas controlled by ISIS, the U.N. panel said civilians were subjected to a “rule of terror” under the group, including massacres, beheadings, sexual enslavement and forced pregnancy.

"The commanders of ISIS have acted wilfully, perpetrating these war crimes and crimes against humanity with clear intent of attacking persons with awareness of their civilian or 'hors de combat' (non-combat) status," the report said, as quoted by Agence France-Presse.

"They are individually criminally responsible for these crimes," it stated, and called on the perpetrators to be brought to justice, for instance before the International Criminal Court.

The panel also said ISIS has denied food and medicine to hundreds of thousands of people in Syria and Iraq.

The report found that ISIS is seeking to "subjugate civilians under its control and dominate every aspect of their lives through terror, indoctrination."

Massacres, beheading boys as young as 15, and amputations and lashings in public squares that residents -- including children -- are forced to watch figure on the list of crimes, as does the widespread use of child soldiers, stoning women to death for suspected adultery and holding women as sexual slaves and forcing them to bear children for the fighters.

One person who fled the group's stronghold Raqqa told investigators he had seen a man punished in a public square for looting.

"Two people held the victim tightly while a third man stretched his arm over a large wooden board. A fourth man cut off the victim's hand," the witness said.

"It took a long time. One of the people who was standing next to me vomited and passed out due to the horrific scene," they added.