Syrian and Russian warplanes carried out dozens of air strikes on rebel-held districts of Aleppo on Friday, a monitor said, as world powers prepared for new talks on a ceasefire.
"Very intense air raids targeted several neighbourhoods from dawn until mid-morning," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
He had no immediate word on casualties.
Ibrahim Abu al-Leith, a spokesman for the White Helmets rescue force in Aleppo, said that air raids had battered the city and its outskirts overnight but had calmed by 11:00am (0800 GMT).
"There are still people stuck under the rubble in (the opposition-held district of) Tariq al-Bab and the rescuers are working to get them out," Abu al-Leith told AFP.
Syria's military had said earlier this month that it would reduce bombardment of eastern parts of the city to allow civilians to leave, but strikes have intensified again this week and left dozens dead.
More than 370 people, including nearly 70 children, have been killed in regime and Russian bombardment of east Aleppo since government forces announced a landmark offensive to take the entire city on September 22.
An estimated 250,000 people still live in eastern parts of Aleppo, under opposition control since mid-2012.
On Thursday, regime ally Moscow said it was prepared to secure safe passage for rebels to leave the war-ravaged second city.
"We are ready to ensure the safe withdrawal of armed rebels, the unimpeded passage of civilians to and from eastern Aleppo, as well as the delivery of humanitarian aid there," Russian Lieutenant General Sergei Rudskoy said.
Russia has faced growing international criticism over the rising civilian death toll in Syria, including Western accusations of possible war crimes.
Since the collapse last month of a truce brokered by Washington and Moscow, Aleppo has been engulfed by some of the worst violence of the five-year conflict.
US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov are expected to hold new ceasefire talks in Lausanne on Saturday along with counterparts from Turkey, Saudi Arabia and Qatar -- all backers of Syrian opposition forces.