UN 'Horror' Report: Syrian Government Beats Thousands to Death

— -- The Syrian government has beaten or tortured to death thousands of detainees since the beginning of the civil war there, “horrors” only rivaled by the war crimes of some rebel Islamist groups like ISIS on the other side of the fight, a new United Nations report says.

“In the Syrian Arab Republic, massive and systemized violence – including the killing of detainees in official and makeshift detention centres – has taken place out of sight, far from the battlefield,” says a report from the UN’s Independent International Commission of Inquiry on Syria, published Monday. “The government has committed crimes against humanity of extermination, murder, rape or other forms of sexual violence, torture, imprisonment, enforced disappearance and other inhuman acts. Based on the same conduct, war crimes have also been committed.”

The report, which the commission says is based on more than 600 interviews as well as “considerable documentary material,” contains some gruesome details of individual cases.

“In early 2014, a detainee at Sednaya prison (Damascus) was killed after guards entered the cell and subjected him to severe beating, including kicking to the head and vital organs. Other prisoners present were ordered to face the wall while the man was heard screaming,” the report says. “The victim was left vomiting blood. A former cellmate explained how the man asked him to tell his wife and family what happened to him.”

The cellmate reportedly said, “He died. We closed his eyes, wrapped him in a military blanket and read the Quran in our hearts.”

Paulo Pinheiro, the commission’s chair, said stories like the cellmate’s were hardly unique.

“Nearly every surviving detainee has emerged from custody having suffered unimaginable abuses,” he said.

The report also named rebel groups, including terrorist designated organizations like ISIS and al Qaeda’s Jabhat al-Nusra, as committing similar atrocities in their own “prisons.”

“Jabhat al-Nusra has set up detention facilities in Idlib [in western Syria] where deaths in detention were documented,” the report says. “The terrorist group also conducted mass executions of captured Government soldiers. Both Jabhat Al-Nusra and some anti-Government armed groups have committed the war crimes of murder, cruel treatment, and torture.”

Likewise, ISIS’s crimes in Iraq and Syria have been well-documented.

Last year ABC News documented alleged abuses perpetrated by Iraqi government forces and pro-Iraqi government militias in Iraq, the evidence of which was available on social media from fighters boasting about the apparent war crimes.

ABC News’ Evan Simon contributed to this report.