This as the United Nations condemned the Islamic State militants and Syria's Bashar al-Assad government for committing war crimes in their fight against eachother.
The new report details human rights abuses committed in the deteriorating state, as observed in interviews and evidence collected between January and July this year.
It said public executions were not rare in northern territories held by Islamic State militants, who would display bodies in public spaces for several days, as part of their campaign of fear.
It added children were being recruited to join in their so-called jihad, or as the U-N put it, "mass atrocities".//
The government of Bashar al-Assad was accused of war crimes, including using chemical agents in 8 separate incidents in April and May this year.
The UN said there was clear proof in some cases that civilian gatherings were deliberately targeted.
Prison detainees, it said, were "subjected to horrific torture and sexual assault."