At least 17 civilians were killed on Saturday in regime and Russian airstrikes on the rebel-held enclave of Eastern Ghouta the capital Damascus, said the Syrian Observatory for Human Rights.
Eastern Ghouta, one of the last remaining opposition strongholds in the country, is the target of near-daily air raids.
The Observatory said Saturday's deadliest strikes had hit the Hammuriyeh district, killing 12 civilians including four children.
An AFP reporter in Hammuriyeh saw residential buildings with their facades blown open, collapsing into streets strewn with rubble.
Residents including members of the White Helmets rescue group rushed to rescue the wounded.
Running past a burning car, one man held a crying boy in his arms, while another carried the apparently lifeless body of a child through the streets.
"I was with other people when a projectile fell nearby," said 33-year-old Mustafa Abu Badr, who was slightly wounded in the head.
"The blast threw me five meters (yards). There were seven wounded and one dead," he said.
Observatory head Rami Abdel Rahman said Syrian and Russian aircraft had "continued their intense bombardment of Eastern Ghouta, targeting several residential areas".
He said those killed also included two people in the district of Madira and three in Erbin, and that 35 people were wounded in the three areas.