The air strikes come after the army of autocratic leader Bashar Assad took over a large portion of eastern Aleppo from rebels in a rapid attack that threatens to crush the opposition in its urban stronghold. The advancement also triggered a mass exodus of Syrian civilians.
Aleppo has been the epicentre of the civil war that began in Syria in 2011 after the regime's crackdown on pro-democracy protests around the country. If captured, rights organisations said it would give Assad and his forces more control and power in the war-torn country.
Assad is being backed by Russia and Iran as he battles to regain the power he once wielded.
"Russian and regime warplanes hit Aleppo's opposition-controlled areas hard, leaving 30 civilians dead and 250 others wounded," an Aleppo-based civil defence official, Baybars Meshaal said.
This is the scene in al-Shaer, east Aleppo today. One of the most important cities in the world - shattered. pic.twitter.com/vJ6OMLEJ9o— Louisa Loveluck (@leloveluck) November 28, 2016
The air strikes mainly targeted the neighbourhoods of Al-Ansari, Al-Sukkari, Al-Qatirgi, Al-Shaar, al-Firdaws, Al-Maadin, and Tariq al-Bab. Meshaal said.
"Russian and regime warplanes have carried out more than 200 air strikes on Aleppo since this morning. We're having trouble reaching the scene due to the intensity of the attacks."
Two rebel officials said they had withdrawn from the northern part of eastern Aleppo to a more defensible front line after losses from fierce bombardment and ground attacks.
The Syrian Observatory for Human Rights said the northern portion of eastern Aleppo lost by the rebels amounted to more than a third of the territory they had held, calling it the biggest defeat for the opposition in Aleppo since 2012.
Thousands of residents were reported to have fled. A rebel fighter said there was "extreme, extreme, extreme pressure" on the insurgents.
US State Department spokesman John Kirby said multilateral talks continued in Geneva on a ceasefire in Aleppo and urged Russia to use its leverage with Assad to stop the bombings.
The Syrian conflict has so far claimed over 400,000 lives and left more than 10 million people homeless, triggering one of history's worst refugee crises in and out of the country.