Militant Islamist fighters take part in a military parade along the streets of northern Raqqa province in June. Reuters

United Nations investigators said Friday that by committing war crimes in Syria, Islamic State group members have violated international humanitarian law. The group, also known as ISIS, used public brutality and indoctrination to control communities, recruit new members and intimidate challengers, according to a recent report by the Independent International Commission of Inquiry on the Syrian Arab Republic. The U.N. ordered ISIS to end the abuse (which included rape, enslavement and torture) immediately.

"By orchestrating systematic harm against a civilian population, ISIS has demonstrated its capacity and intent to willfully [sic] apply measures of intimidation and terror, such as violence to life and inhuman treatment inflicting great suffering and injury to bodily integrity," the report read. "ISIS has beheaded, shot and stoned men, women and children in public spaces in towns and villages across northeastern Syria." With information from more than 300 interviews with men, women and kids who lived in ISIS-dominated areas, the report sought to "bring to light the voices of Syrians who ISIS has sought to silence," it read.

Aleppo, Raqqa, Deir el-Zour and Al-Hasakah were mentioned by name in the report, which asserted that more than 200,000 people have been displaced in efforts to avoid ISIS violence since April 2013. The report recommended world leaders hold the ISIS members accountable for their actions against humanity. Commanders should be seen as individually responsible for their crimes, which include "takfir," or declaring people immoral to justify attacking them.

The committee specifically took issue with ISIS' public humiliation of victims, Reuters reported. The group displayed bodies to scare others into submission. "Following the killings, the corpses are placed on public display, often on crosses, for up to three days, serving as a warning to local residents," it read. "Witnesses saw scenes of still-bleeding bodies hanging from crosses and of heads placed on spikes along park railings."

The report concluded with several pleas to the international community, including for nations to stop selling weapons to ISIS members, prioritize keeping kids and women safe, and stop the group from committing more crimes.