Warplanes targeted rebel-held areas of eastern Aleppo on Friday in a second day of heavy bombardment.
The new strikes come hours after the army announced the start of a military operation there, rescue workers and activists said.
The Syrian military, which is backed by the Russian air force, said late on Thursday it was starting a new operation against the rebel-held east, which is home to at least 250,000 people and was also targeted in heavy air strikes on Thursday.
Those strikes reportedly resulted in 24 deaths.
The Syrian military could not immediately be reached for comment on Friday, and there was no word on casualties.