BEIRUT: Rebel rocket fire killed at least 34 civilians in Aleppo an activist group said Tuesday.

Twelve children were among the dead as Islamist rebel factions pounded western neighborhoods of the city with more than 300 rockets Monday, the British-based activist group the Syrian Observatory for Human Right said. 

Control of the city is divided between rebels in the east, and forces loyal to President Bashar al-Assad in the west.

Both sides frequently bombard each other but Observatory director Rami Abdel Rahman told AFP that Monday's deaths marked "one of the highest tolls in opposition attacks in Aleppo city." 

"The number of deaths is likely to rise, as there are roughly 190 people wounded, including dozens in critical condition with serious wounds," he said. 

"With dead and wounded combined, it adds up to the most violent day for government-controlled parts of Aleppo city in the whole war."

The rocket fire came as U.N. peace envoy Staffan de Mistura arrived in Damascus for fresh talks with government officials on ending the four-year conflict. 

Last year, de Mistura proposed a "freeze" on fighting in Aleppo as a first step towards local ceasefires across Syria. 

But the rebels rejected the proposal and the government has continued to pound rebel-held areas of the city with deadly air strikes.

The conflict began with anti-government demonstrations in March 2011 but has evolved into a multi-front war that has left more than 230,000 people dead.