The UN voiced alarm Thursday (November 29th) over renewed Russian air raids on Idlib, warning the strikes risk setting off "a gigantic power keg", AFP reported.

"We are very worried for recent developments," Jan Egeland, the head of the UN Humanitarian Taskforce for Syria, told reporters.

A 10-week-old Idlib truce deal hangs in the balance after an alleged chemical attack in the government-held city of Aleppo on Saturday, which triggered retaliatory raids.

The exact circumstances of the attack on three districts of Aleppo remain murky and bitterly disputed.

The Syrian government has blamed fighters in neighbouring Idlib for the attack, which the Syrian Observatory for Human Rights said hospitalised 94 people.

In his final press conference before stepping down on Friday, Egeland stressed that if a chemical attack is confirmed, "it is a war crime".

At the same time, he described the escalation around Idlib, and the first air raids on the area since mid-September, as "very serious".

"Over recent days we have seen provocations and counter-provocations, exchanges of mortars and grenades... We have seen increasing incursions in both directions," he said, warning that "this is the worst possible kind of action in the worst possible place."

"It is really playing with a gigantic powder keg in the middle of three million civilians," he said.