The air strikes, which began yesterday and continued today, killed 45 civilians in and around Aleppo and 22 in neighbouring Idlib province, the Syrian Observatory for Human Rights said.
The raids came as the Islamist Faylaq al-Sham Islamist faction, part of the rebel alliance, said it had begun a new offensive "to liberate" the regime-held district of Zahra on Aleppo's western outskirts.
The Britain-based Observatory and opposition fighters said a car bomb exploded in Zahra Sunday, but did not mention casualties.
"The intensification of the strikes in Idlib is due to the fact that this province is the main source of fighters for the Army of Conquest," said Observatory head Rami Abdel Rahman.
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An AFP correspondent in rebel-held eastern Aleppo said the strikes were especially intense around the southern district of Ramussa, seized by rebels earlier this month in a major setback for forces loyal to President Bashar al-Assad.
Nine other civilians were killed in rebel shelling of regime-held western Aleppo Saturday, the Observatory said.
Fighting for the city has intensified after regime troops seized control of the last supply route into rebel-held areas in mid-July.
After a nearly three-week siege, rebels took Ramussa on August 6, linking up with opposition-held neighbourhoods.
Emboldened by the success, the Army of Conquest announced an ambitious bid to capture all of Aleppo, which if successful would be the biggest opposition victory yet in Syria's conflict.
Alliance fighters late today began an assault southeast of Ramussa on an area containing a former cement plant turned into an army barracks, where a large amount of weapons and military vehicles are stored, the Observatory said.
The increased fighting has raised concerns for the estimated 1.5 million civilians still in Aleppo, including some 250,000 in rebel-held areas.
The United Nations has called for regular 48-hour pauses in the fighting to allow aid into the city, which has suffered from severe shortages of food, water and medical supplies.
Russia began air strikes last September in support of Assad, helping the regime to consolidate its hold on loyal areas and regain some territory.
The defence ministry in Moscow said Sunday six long-range bombers from Russia had struck around Deir Ezzor, a stronghold of the Islamic State group.