The Syrian government warplanes pounded rebel-held districts of Shaar and Sakhur in the northern city of Aleppo on Sunday, a watchdog said.
"Fighter jets are being used to pound Shaar and Sakhur," Rami Abdel Rahman of the Syrian Observatory for Human Rights told AFP.
According to the UK-based observatory, clashes broke out earlier between troops and rebels in the districts of Ansari, Hamdaniyeh and Sukari in Aleppo, scene of heavy fighting since July 20, adding at least 44 people were killed across Syria on Sunday.
Of those killed, 28 were civilians, 10 were soldiers and six were rebel fighters.
In Damascus, regime forces raided the district of Qaboon on Sunday, arresting several civilians, adding that one of the detainees was a 12-year-old boy, claimed the observatory.
After clashes with rebels in Rokn Eddin on Saturday, the military set up new checkpoints in the neighbourhood of Damascus and in several other parts of the capital.
Elsewhere in the province of Damascus, clashes broke out in Kfar Batna as regime forces shelled that village. The army also shelled Harasta, in the same province.
At Rastan in the central province of Homs, regime forces pounded rebel positions, said the observatory.
"Regime forces dropped more than 60 shells on Rastan, at a rate of four to five shells a minute," the watchdog added.
On Saturday, violence nationwide killed 205 people, the observatory said.
It is impossible to independently verify death tolls out of Syria, while the United Nations has stopped giving its own count.