Intense government air strikes and artillery fire killed at least 27 people on Saturday in rebel-held parts of
Syria's Aleppo, where hospitals have been destroyed and schools forced to close.
An AFP correspondent described relentless bombardment with air strikes, mortar rounds and barrel bombs slamming into residential neighbourhoods in the east of the battered second city.
"It is a catastrophic day in besieged Aleppo with unprecedented bombardment with every type of weapon," a member of the White Helmets rescue group said in a video posted on the organisation's Facebook page.
"People went to sleep to the sound of bombardment and awoke to the sound of bombardment," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, a Britain-based monitor of the war.
Syrian government troops began a new assault on the rebel side of Aleppo on Tuesday, as they renewed their bid to recapture the east of the city. Once Syria's economic powerhouse, Aleppo has been ravaged by the war that has killed more than 300,000 people since it began with anti-government
protests in March 2011.
The city has been divided between government control in the west and rebel control in the east since mid-2012. More than 250,000 people remain in the opposition-held part of the city, which has been besieged by the regime since July. The intensity of the bombardment has forced residents to stay indoors, leaving streets all but deserted.