The UN has accused the Syrian government and rebels opposed to it of committing war crimes in Syria.

A report released by the Independent International Commission of Inquiry on the Syrian Arab Republic details abuses by Islamic State and other rebel groups fighting Bashar al-Assad’s regime.

The government is thought to have conducted chemical attacks eight times this year alone and used barrel bombs on civilian areas.

"In some instances, there is clear evidence that civilian gatherings were deliberately targeted" by government forces, the investigators said.

"In government prisons, detainees were subjected to horrific torture and sexual assault."

IS is accused of waging a campaign of fear in the areas it controls, including public executions, whippings, amputations and the recruitment of children.

"Bodies of those killed are placed on display for several days, terrorising the local population," the document says.

"Women have been lashed for not abiding by IS's dress code. In Raqqa, children as young as 10 are being recruited and trained at IS camps."

Paulo Pinheiro, the chairman of the UN panel, said the international community has failed "in its most elemental duties - to protect civilians, halt and prevent atrocities and create a path toward accountability".