Syrian regime forces advanced Sunday (October 2nd) in Aleppo with the help of Russian airstrikes, as the UN's top aid official decried the "living hell" suffered by residents in the city's rebel-held east, AFP reported.

The Syrian army announced a major push on September 22nd to capture Aleppo's opposition-held east and has gained ground in the city with the help of ally Moscow.

Dozens of airstrikes pounded multiple battlefronts in the city throughout Sunday but lessened as evening fell.

The Syrian Observatory for Human Rights said rebel groups and regime forces exchanged artillery fire in several neighbourhoods across Aleppo.

The monitor said Russian raids "helped regime forces to advance in the north of the city", where they reached the outskirts of the opposition-held Al-Heluk district.

Assad's Russian-backed military campaign in Aleppo has sparked international outrage, particularly after two barrel bombs hit the largest hospital in the city's east on Saturday.

UN aid chief Stephen O'Brien fiercely criticised the attack on the M10 hospital, and called on Sunday for immediate action to end the "living hell" of civilians in Aleppo's east.

"The health care system in eastern Aleppo is all but obliterated. Medical facilities are being hit one by one," O'Brien wrote.