The United Nations aid chief warned Thursday, September 29 that Aleppo faces a humanitarian catastrophe "unlike any" witnessed so far in Syria's brutal five-year war, AFP reports.

"Let me be clear: east Aleppo this minute is not at the edge of the precipice," Stephen O'Brien told the Security Council.

"It is well into its terrible descent into the pitiless and merciless abyss of a humanitarian catastrophe unlike any we have witnessed in Syria," said the UN undersecretary-general for humanitarian affairs.

The council was meeting to discuss the crisis in Syria as France said it would push for a UN resolution imposing a ceasefire in Aleppo, which has been under fierce bombardment by Syrian and Russian warplanes for a week.

U.S. Ambassador Samantha Power described the escalation as "the most savage week we've seen in an incredibly savage five-plus-year war," with more than 1,000 people killed by 1,700 air strikes on east Aleppo alone.

Power described the latest offensive as "soul-shattering" and accused Russia and Syrian President Bashar al-Assad of "unleashing a savagery" against civilians.

"We're at a turning point," she said.

O'Brien appealed for action from the council after diplomatic efforts on the sidelines of last week's General Assembly meeting ended in failure, triggering a new upsurge in violence on the ground.

"This revolting situation in Aleppo must, please, be the SOS, the May Day call, to the international community," he said.

"Syria is bleeding. Its citizens are dying. We all hear their cry for help."

More than 100,000 children remain trapped in rebel-held east Aleppo, which has come under intense bombing since the Syrian army announced on September 22 an offensive to retake the city.