A twin car bombing near the northern Syrian city of Aleppo killed a senior leader of an Islamic rebel brigade opposed to an al Qaida-linked faction, activists said.
Helicopters have pounded Aleppo for weeks with barrel bombs - crude containers packed with explosives, fuel and scraps of metal.
Government airstrikes hit at least four different areas of the city on Sunday, including near a mosque and a vegetable market, activists said.
The Syrian Observatory for Human Rights monitoring group said the hardest-hit neighbourhood was Tariq al-Bab, which was targeted at least eight times on Sunday alone. Activists said one strike killed 10 people.
Syrian forces have inched into eastern neighbourhoods of Aleppo in recent weeks, their most important advance there since rebels fighting to overthrow President Bashar Assad seized the areas in mid-2012.
Activists said the airstrikes coupled with shelling have cleared the way for the government to advance and forced civilians and rebels to flee.
That conflict may escalate after a twin suicide bombing killed 26 people on Saturday, including a senior military commander of a prominent rebel group, the Tawhid Brigade.
The attack targeted the base of its rivals in the Tawhid Brigade and killed senior leader Adnan Bakkour, said Observatory director Rami Abdurrahman.
The Islamic State also killed another prominent commander, Abu Hussein al-Dik of Suqour al-Sham, on Saturday near the central city of Hama, the Observatory said.