A napalm-like substance was used to bomb a crowded playground in northern Syria, killing at least 10 children.
A jet fighter, believed to be part of President Assad's airforce, dropped an incendiary bomb onto an Aleppo school leaving many children with severe burns all over their bodies, a BBC Panorama programme reported.
Graphic footage captured by the television crew showed adults and children being rushed to a local hospital, their clothes burnt and skin coated in a white substance.
"They arrived like the walking dead," journalist Ian Pannell says in the report, suggesting a substance like napalm or thermite was contained in the bomb.
Eyewitnesses said the jet hovered over the school numerous times, probably searching for a target, before it dropped the device.
The attack killed more than ten people and left many more seriously wounded, the BBC said.
The school's headmaster, who preferred not to be identified, said it was the most horrific sight he had ever witnessed.
"We have seen images on TV, we have heard many stories, but we have never seen anything like this before."
"The worst thing in life is watching someone die right in front of you and you can't do anything.
"There were dead people, people burning and people running away, but where to? Where would they go? It is not safe anywhere. That is the fate of the Syrian people."
A British medic, Dr Rola, working in the area with the charity Hand In Hand, treated some of the victims. She also suggested napalm might have been used.
"It is just absolute chaos and carnage here. We have had a massive influx of what looks like serious burns, seems like it must be some sort of, not really sure, maybe napalm, something similar to that.
"But obviously within the chaos of the situation it is very difficult to know exactly what is going on."
Napalm is not considered a chemical weapon but its use is forbidden in civilian areas by international conventions.
The BBC report came as British MPs vote against military intervention, carrying a humiliating blow to PM David Cameron.
The US replied to the vote saying it will continue efforts to put up an international coalition against Bashar al-Assad but President Barack Obama will take the final decision on the course of future actions.
"The US will continue to consult with the UK government - one of our closest allies and friends," the White House said.
"As we've said, President Obama's decision-making will be guided by what is in the best interests of the United States."
"He believes that there are core interests at stake for the United States and that countries who violate international norms regarding chemical weapons need to be held accountable."