"The number of people killed in air strikes on the village of Hammuriyeh has risen to 42, including six children," said the Syrian Observatory for Human Rights.
Earlier, the Britain-based group had given a toll of 32 dead and denounced what it called a "massacre".
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According to the Local Coordination Committees (LCC), a grassroots network of opponents, one of the strikes hit a square in Hammuriyeh where people had gathered for the weekly Muslim Friday prayer.
Syria's air force began launching strikes against opposition-held areas in the summer of 2012, with rights groups blasting the regime for attacks they say fail to discriminate between civilian and military targets.
The rebel-held Eastern Ghouta area, located east of Damascus, has been under a suffocating army siege for more than a year, leaving tens of thousands of civilians short of food and medical supplies.