Video report by ITV News Correspondent Paul Davies
Syrian state forces have faced fresh accusations of war crimes after they bombarded civilians with 'thermite bombs'.
Women and children were among those who suffered deep burns in a fresh assault on the rebel-held stronghold of Idlib.
Thermite is said to be the hottest burning substance in the world - burning at temperatures of 2,500C.
Opposition fighters in the area had been celebrating only hours earlier after breaking a siege in the neighbouring city of Aleppo where civilians had faced starvation and dwindling medical supplies.
But their joy was short-lived as the state and its Russian allies hit back after the rebels' win by raining down blasts in the region.
On Sunday night the blasts in Idlib lit up the sky with an eerie white glow which aid workers and opposition figures say points to the use of substances illegal under the Geneva Convention.
A woman and two children were among those to have suffered "deep, deep burns" in the attack, according to emergency workers in the area.
A spokesman for the opposition's volunteer rescue organisation, the White Helmets, said that a government bombing campaign in Aleppo had only added to what was already a "humanitarian crisis" within the besieged city.
Syrian government forces released cockpit videos showing some of the latest attacks on rebel positions.
But the repeated targeting of civilian areas and the alleged use of banned weapons have led to fresh accusations of war crimes.
There have been calls for the UN to take action at a special hearing on Aleppo taking place in New York tonight.
Among those testifying was Dr Samer Attar, a US citizen who recently volunteered in Aleppo. He has spoken to ITV News about the "horrifying" conditions in Aleppo and described the situation as "desperate and dire" for medical staff still in the city.
Dr Attar said he hoped that the UN talks would add a "sense of urgency" at the global body as he pushed for action.
"Being silent, being indifferent, being apathetic, being ignorant - that does not make things better," he said.