A pregnant woman and three children were among 18 civilians killed when Syrian fighters shelled a Kurdish neighbourhood in the northern city of Aleppo, according to a monitoring group.
The Britain-based Syrian Observatory for Human Rights (SOHR) said 70 people, including 30 children, were also wounded in Tuesday's attack, adding that the shelling was a violation of a ceasefire agreement.
The shelling targeted Sheikh Maqsud area, where up to 50,000 residents are caught in the crossfire of government-held districts and those controlled by oppposition fighters.
In a separate incident on Tuesday, fighters belonging to the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) launched attacks on government-held areas near Damascus in an apparent response to the group's loss of ground elsewhere in Syria.
An ISIL statement said the group attacked the Tishrin power station 50km northeast of the capital and a Syrian military source acknowledged confirmed the assault but said all those who took part had been killed.
The source said the attack appeared to be ISIL's response to reverses suffered by ISIL around Palmyra.
Syrian and allied forces, backed by Russian air strikes, have forced ISIL fighters out of the town of al-Qaryatain, 100km west of the ancient city of Palymrya, itself recaptured by the government last week.
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Russian forces have helped remove more than 1,500 mines in Palmyra since it was taken over, Maria Zakharova, Russian foreign ministry spokesperson, said on Wednesday.
Elsewhere on Tuesday, SOHR said ISIL fighters, using five bomb-laden cars, struck military positions near the airport, southeast of Damascus, killing 12 soldiers.
Government forces responded with shelling and air strikes in that area, and jets also struck the town of Dumeir, 40km northeast of Damascus, which is held by a group sympathetic to ISIL.