At least 38 people, including 14 children, were killed on Tuesday when Syrian insurgents shelled three government-held neighborhoods in western Aleppo, the Syrian Observatory for Human Rights said.
"More than 150 people were wounded. This is one of the highest death tolls caused by rebel shelling on regime areas in the city," Rami Abdelrahman, the head of the Observatory, told Reuters.
Abdelrahman said insurgents bombarded the neighborhoods with dozens of mortars and rockets.
In retaliation, regime air strikes killed more than 10 civilians in rebel-held neighborhoods, activists said.
Activists claim the Syrian military frequently uses helicopters to drop crude barrel bombs – giant canisters packed with hundreds of pounds of explosives and scrap metal – on rebel-held towns and neighborhoods.
President Bashar al-Assad has denied the use of barrel bombs by the Syrian military.