Syrian military planes pounded a rebel-held area of the northern city of Aleppo on Wednesday as opposition fighters claimed to have seized parts of a town on the Iraqi border, a watchdog said.
Twelve people were also killed by troops in a raid on a Damascus district, according to the Syrian Observatory for Human Rights, a day after it reported dozens killed when regime forces stormed another suburb of the capital.
It said rebel fighters had seized control of an intelligence office and checkpoints in the eastern town of Albu Kamal on the Iraqi border.
"The rebels have seized parts of the town, including several checkpoints," Observatory director Rami Abdel Rahman told AFP. "But it would be very hard for the rebels to take the whole of it, because there are hundreds of regime forces deployed there."
In Aleppo, fighter jets struck the southern district of Sheikh Saeed after regime forces and rebels clashes near a missiles depot in the area, the Observatory said.
Elsewhere in Syria's second city -- now the epicentre of the 17-month conflict -- the army shelled several other rebel-held districts, including Shaar, Sakhur and Hanano in the east, the Observatory said.
It said 31 civilians, including five women and five children, had been killed in shelling on the northern commercial hub on Tuesday.
In all, a least 198 people were killed on Tuesday, said the Observatory, which has a network of monitors on the ground. Among them were 127 civilians, 20 rebel fighters and 51 soldiers.
The Britain-based watchdog also said 12 men were killed by gunfire and shelling during a military raid Wednesday on the southwestern Damascus district of Kfar Sousa.
On Tuesday, the army had stormed Maadamiyat al-Sham, a suburb west of Damascus, the Observatory said, and killed dozens of people, many of them shot dead or summarily executed.
It said it had documented the names of at least 42 civilians killed there, while many more were killed when the army targeted a funeral procession.
"Initial reports say that the army targeted a funeral procession, killing at least 36 people," said the watchdog.
The mixed suburb is home to about 200,000 people including Christians, Alawites and Sunni Muslims.
The Observatory also said that dozens of unidentified bodies had been found in a basement in Maadamiyat al-Sham on Tuesday, the latest grisly find as the 17-month conflict becomes increasingly brutal.
More than 23,000 people have been killed in Syria since the outbreak of an anti-regime revolt in March last year, according to the Observatory. The UN puts the death toll at 17,000.
It is impossible to verify the figures.