International medical charity Medecins Sans Frontieres said on Saturday that at least 70 people had been killed in a missile attack on a marketplace near Damascus the day before.
A monitoring group, which had put the toll at 57, said bombardments continued in the area, and that another six people were killed by government air strikes on Saturday morning.
The bombardments came as air raids by Syrian government forces and Russian warplanes intensified across the country.
Moscow's month-old military intervention in support of President Bashar al-Assad has alarmed the United States and its allies, as world powers step up diplomatic efforts to end the war.
Syrian government forces fired missiles into a marketplace in the town of Douma northeast of Damascus on Friday in the bloodiest attack on the area for weeks, the Syrian Observatory for Human Rights said.
MSF said a strike on a hospital on Thursday, which itself had killed 15 people, caused damage to medical facilities that made it difficult for paramedics to treat the wounded from the marketplace bombing the following day.
"MSF fears the intensification of bombing that has been seen in northern and central Syria over the course of October could become even more horrific if it spreads to besieged areas around Damascus, where almost a million people are trapped," it said in a statement.
On Saturday, at least 15 air strikes hit the area, the Observatory said.
Syria's four-year-old conflict has killed an estimated 250,000 people and driven more than 11 million from their homes.
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