Nearly 500 civilians have been killed in both government-controlled and rebel-held Aleppo since the middle of November, a monitoring group reported Thursday.
The Britain-based Syrian Observatory for Human Rights said 384 civilians, among them 45 children, have been killed as a result of airstrikes and shelling by Syrian government forces and its allies on the rebel-held side of eastern Aleppo.
On the government-held side, 105 people, including 35 children, were killed by rebel shelling.
The number of rebel fighters killed since November 15 is 309, according to the report.
The rebel enclave of the Syrian city has been shrinking dramatically in recent weeks, amid a quick advance by government forces and its allied militias, including the Lebanese Hezbollah movement.
The opposition is now confined to a small area, estimated to be just 20 per cent of the original territory it held in the city.
Six Western powers demanded on Wednesday an "immediate ceasefire" to bring aid into rebel-held Aleppo, warning "a humanitarian disaster" is unfolding and war crimes were being committed.
The government and Russia have indicated they would only accept a surrender by the embattled rebel forces, calling on them to agree to leave the territory.
The International Committee of the Red Cross said nearly 150 civilians, "including many patients in need of urgent care," were just evacuated from the Old City of Aleppo, which government forces seized this week.
Residents in the rebel-held districts report shortages of food, clean drinking water and medicines and say there are regular airstrikes and shelling. People are crowding into apartments in the remaining areas.
