The UN has said that Syrian opposition fighters may have committed war crimes.

A video, which appears to show the execution of Syrian soldiers, surfaced after rebels seized army checkpoints all over Syria.

The video shows rebels assaulting captured soldiers, before shooting at the cowering group.

The spokesperson of the UN High Commission for Human Rights, Rupert Colville, said on Friday that it looked like the victims "were no longer combatants and therefore, at this point, it looks very like a war crime".

"Unfortunately this could be the latest in a string of documented summary executions by opposition factions as well as by government forces and groups affiliated with them, such as the (pro-government) Shabiha militia.

"The people committing these crimes should be under no illusion that they will escape accountability, because there is a lot of accumulated evidence, perhaps including this video," he said.

Amnesty International condemned the killings and said in a statement,

"This shocking footage depicts a potential war crime in progress, and demonstrates an utter disregard for international humanitarian law by the armed group in question."

“Amnesty International has so far been unable to confirm the identity of the armed group that carried out these summary killings, and no group has yet claimed responsibility. But we will continue to investigate the incident and once again urge all sides to respect the laws of war and to refrain from torturing, ill-treating or killing their prisoners.”