Intense air and missile strikes on a school district and other areas in insurgent-held Damascus suburbs killed dozens of people on Sunday, including children, a monitoring group and local rescue workers said.
The Syrian Observatory for Human Rights said unidentified war planes hit the town of Douma, 10 miles northeast of the capital, and surface-to-surface missiles fired by the Syrian army also hit the surrounding areas, including Eastern Ghouta.
The organization put the death toll at 28 civilians, including at least two children and a school principal.
Syrian Civil Defense, a humanitarian rescue group that operates in rebel-held areas, put the death toll at 35 and said many others were wounded. It posted a photo of a dead baby with a severe wound to its head.
Issam al-Rayyes, spokesman for the Southern Front of the insurgent Free Syrian Army, said as many as 60 people had been killed in strikes on the Douma area which started early on Sunday.
Many of Douma's residents have fled the nearly five-year conflict, moving to nearby rural areas. Syria's civil war, which began as an uprising against President Bashar al-Assad, has killed more than 250,000 people and driven more than 10 million from their homes.
The areas have been under heavy bombardment in recent months. The Syrian army has said its strikes target insurgents that have launched attacks on government-held areas.
The Observatory, which has gathered information from a network of contacts on the ground since the start of the conflict in 2011, said at least 40 mortar bombs fired by insurgents in the eastern suburbs hit Damascus on Sunday.
State news agency SANA said three civilians had been killed and at least 30 wounded in mortar attacks targeting residential neighborhoods of Damascus. Most of the victims were school students, it said, citing its reporter in the area.
Assad said on Friday he would not negotiate with armed groups, appearing to scupper peace talks that Russia and the United States hope to bring about next month.
Washington helped broker an agreement reached on Thursday by more than 100 members of Syria's opposition parties and more than a dozen rebel fighting groups –to send a joint team to meet the government under U.N. auspices next month.
Al Jazeera with wire services