Six children were among the dead in Eastern Ghouta, the largest rebel bastion near Damascus, the Syrian Observatory for Human Rights said.
"It was a series of air strikes throughout the day and the death toll may still rise," the Britain-based group added.
He said civilians had died in Jisreen, Kafr Batna and the largest of the towns in Eastern Ghouta, Douma.
An AFP photographer in Douma saw half a dozen wounded children sitting on the floor of a makeshift clinic, caked in dust and blood as they awaited treatment.
Another AFP photographer in Saqba saw residents scrambling over rubble and through clouds of dust, tossing debris aside as they searched for signs of life.
One man sat atop a small mountain of cinderblocks, clothes, and furniture with his head in his hands.
The Observatory said today's bombardment brought to 49 the number killed in Eastern Ghouta in two days of attacks.
"There has been fierce artillery shelling and air strikes since yesterday, and 165 people total have been wounded," Observatory chief Rami Abdel Rahman said.
It is the last remaining opposition stronghold near Damascus, where a string of local "reconciliation deals" have seen villages and towns brought back under the control of President Bashar al-Assad's government.
Hundreds of people were killed in Eastern Ghouta in chemical weapons strikes allegedly carried out by government troops in August 2013.
Today, at least 58 people were killed in a suspected chemical attack on the northwestern Syrian town of Khan Sheikhun, according to the Observatory.
Dozens more suffered respiratory problems and symptoms including vomiting, fainting and foaming at the mouth, the monitor and doctors at the scene said.
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