Three civilians were killed when rebels shelled government-held areas of Aleppo city in northern Syria on Sunday, a monitoring group said.
The Syrian Observatory for Human Rights said that another 15 civilians were injured in the shelling, which came on the second day of a temporary truce in the city announced by the government's Russian ally.
The Britain-based Observatory, which monitors violence through a network of activists across the country, also reported that 75 pro-government fighters had been killed while beating back a rebel offensive on government positions in the city on Tuesday and Wednesday, before the truce announcement.
Violence has simmered since April 22 in Aleppo, with at least 286 civilians killed in reciprocal attacks by regime forces and rebels, according to the Observatory.
The dead included 50 people killed in a government air raid that hit a hospital, among them the last paediatrician still working in the rebel-held east of the city.
In mid-April the Syrian opposition suspended its participation in peace talks in Geneva, citing a lack of progress on humanitarian issues and escalating ceasefire breaches.