A civil defense worker said at least 32 people were killed in the rebel-held parts of the city during the air strikes, with 18 bodies pulled from flattened buildings in the Qatrji neighborhood, the worst hit.
The monitor said dozens of barrel bombs - oil drums or cylinders packed with explosives and shrapnel- were dropped by helicopter on densely populated districts.
"This week-long campaign of bombing is very intense and day by day it's getting worse ... it is the worst we have seen in a while," said Bebars Mishal, a civil defense official in rebel-held Aleppo.
For their part, rebels hit government-held areas of Aleppo in what Syrian media said was an escalation of mortar attacks on the western districts.
State media said attacks on June 5 on Hamadaniyah, Midan and other neighborhoods by insurgents killed at least 20 people, in the second day of intense shelling of government-held areas. The death toll over the whole weekend was at least 44.
Aleppo, the country's largest city before the war, has been divided for years between rebel and government-held zones.
Full control of Aleppo would be a huge prize for President Bashar al-Assad. Russia's military intervention since September has helped to bolster Assad's government.