Syrian regime air strikes in the opposition-held town of Douma near Damascus, and Aleppo in the north killed 25 people on Saturday.
Regime bombardment on Douma killed 13 people, according to the Syrian Observatory for Human Rights (SOHR), while opposition sources said 12 civilians were killed in opposition-held neighbourhoods in Aleppo.
SOHR, which monitors the Syrian war through a network of contacts, said the death toll in Douma, northeast of the capital, was expected to rise because more than 22 others were injured, some critically.
There was also fighting near Bala southeast of Damascus between opposition groups and regime forces with deaths occurring on both sides, the Observatory said.
The barrage of air strikes on Aleppo began around 10:00 am (0700 GMT) on several neighbourhoods, including the heavily-populated Bustan al Qasr district.
It was the second day of deadly strikes on Aleppo.
On Friday, 25 civilians were killed and another 40 wounded in regime air strikes on opposition-controlled parts of Aleppo.
A cessation of hostilities deal which went into effect on Feb. 27 almost completely collapsed recently as mediators have struggled to get combatants to honour the deal to enable peace talks in Geneva to proceed.
On Friday, UN Special Envoy to Syria Staffan de Mistura vowed to take the talks into next week despite a walkout by the main opposition High Negotiations Committee (HNC) in protest against the worsening situation on the ground.
The opposition's coordinator at the Geneva talks, Riad Hijab, said earlier it was unacceptable for talks to go on if the regime and its allies pushed on with sieges and bombing civilian areas.
UN Special Envoy to Syria Staffan de Mistura said on Thursday that around 400,000 people have been killed in Syria's five-year war.