The strikes, which began on Saturday and were continuing on Sunday, killed at least 45 civilians in Aleppo and west of the city and 22 more in neighbouring Idlib province, a monitoring group said.
The Syrian Observatory for Human Rights said the strikes were targeting areas held by the Army of Conquest, an alliance of rebel, Islamist and jihadist forces that has mounted a major offensive to seize Aleppo.
"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," the head of the Britain-based Observatory, Rami Abdel Rahman, told AFP.
An AFP correspondent in rebel-held eastern Aleppo said the strikes were especially intense around the southern district of Ramussa, seized by rebel fighters 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 on Saturday, the Observatory said.
Aleppo, Syria's former economic hub and a focal point of the country's five-year civil war, has been divided between a rebel-held east and regime-controlled west since mid-2012.
Intensifying battle
Fighting for the city has intensified this summer, after regime troops seized control of the last supply route into rebel-held areas in mid-July.
After a nearly three-week siege, rebel forces took Ramussa on August 6, linking up with opposition-held neighbourhoods.
Emboldened by the win, 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.
The increased fighting has raised deep concerns for the estimated 1.5 million civilians still in Aleppo, including some 250,000 in rebel-controlled 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 launched 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 that six long-range bombers from Russia had struck around Deir Ezzor, a stronghold of the Islamic State group in Syria.
IS controls large parts of Deir Ezzor city and most of oil-rich Deir Ezzor province in the east of the country -- part of the swathes of territory in Syria and Iraq that the group seized in mid-2014.
The ministry said in a statement that the Russian Tupolev bombers carried out raids to the southwest, east and northeast of the city, wiping out two command posts, six arms depots, IS vehicles and "a large number of fighters".
IS emerged amid the chaos of Syria's conflict, a complex and multi-front war that has left more than 290,000 dead and forced millions from their homes since beginning with anti-regime protests in March 2011.
Girl evacuated
A US-led coalition is also battling IS in Syria and Iraq, with air strikes and backing for the Syrian Democratic Forces, an Arab-Kurdish militia alliance, which on Friday took full control of the strategic city of Manbij after an IS retreat.
The jihadists took some 2,000 civilians as they fled to serve as human shields. Hundreds were released on Saturday but the SDF said the fate of many remained unclear.
Kurdish television showed footage of jubilant civilians in Manbij, including smiling mothers who had shed their veils and men who had lived for weeks under a shaving ban cutting their beards.
In rare good news from the conflict, a 10-year-old girl who was shot in the besieged town of Madaya was evacuated to a Damascus hospital where she was in a stable condition, the Observatory and a Syrian security source said.
Ghina Quwayder's leg was shattered when she was shot by a government sniper at a checkpoint in the southwestern town earlier this month while buying medicine for her mother, according to Amnesty International.
The rights group had launched a campaign urging help for the girl to be evacuated. The Syrian Red Crescent was able to bring Ghina and her mother Sahar to Damascus after midnight on Sunday.