Nearly 30 civilians including several children were killed and dozens wounded in the raids by Russian warplanes and regime aircraft, the Syrian Observatory for Human Rights, a Britain-based monitoring group, said.
The intensity of the bombardment, which included artillery barrages and barrel bombings by helicopters, brought new misery to the estimated 250,000 civilians besieged by the army.
The escalation came after US Secretary of State John Kerry failed to reach an agreement with Russian counterpart Sergei Lavrov on terms to salvage a failed ceasefire.
A US official told AFP that no Kerry-Lavrov meeting had yet been scheduled for Friday, "but that could change".
An AFP journalist in rebel-held east Aleppo reported relentless air raids and artillery fire overnight and Friday morning.
Entire apartment blocks were flattened, overwhelming rescue teams from the White Helmets civil defence organisation.
In the Al-Kalasseh district, three buildings were levelled by a single strike, and rescue workers were trying frantically to reach survivors using a single bulldozer and their bare hands.
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