The Syrian army shelled rebel-held districts of commercial capital Aleppo on Monday as violence nationwide killed 37 people, 27 of them civilians, a human rights group said.
Ten people were killed in Aleppo, eight of them civilians, the Syrian Observatory for Human Rights said.
Clashes broke out in the southwestern district of Salaheddin, where a rebel commander was killed on Monday morning after three tanks moved in on Sunday evening, the Britain-based watchdog said.
"Rebels and regime forces also clashed fiercely in the Shaar, Hanano and Sakhur districts," it said.
The army bombarded the Palace of Justice, as well as the Marjeh and Shaar districts. In Bab al-Nayrab, troops shot dead a civilian while he was helping wounded people, it added.
In Damascus, clashes broke out in the Sheikh Ibrahim area of Rokn Eddin district, where four civilians were killed.
"Regime forces gave residents an ultimatum to leave the neighbourhood, which sparked fears that the area would be shelled," said Observatory director Rami Abdel Rahman Abdel Rahman.
Syrian state television said that "security services seized a den of terrorist mercenaries in the neighbourhood," capturing a variety of weapons.
The security forces "clashed with the terrorists, killing a number of them and arresting others, while the rest threw down their arms and surrendered," the television said.
The army had said on Saturday that it had "cleansed all the districts of Damascus," after retaking the last rebel-held neighbourhood Tadamun in heavy fighting.