"The number of people killed has risen to 20 including two children, a teenager, a woman and a media activist," said the Syrian Observatory for Human Rights.
The Syrian Revolution General Commission, a network of activists on the ground, described the bombing as a "massacre".
"The raid targeted a crowded market where people were buying vegetables and home appliances," it said. "Many buildings have been damaged, and one collapsed."
Warplanes have launched rockets and helicopters dropped so-called barrel bombs, often on densely populated areas, terrorising residents of rebel-held areas.
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Human rights organisations as well as Arab and Western countries have condemned the offensive as "indiscriminate" and "unlawful," while Assad's regime says it is targeting "terrorists".
Activists said Ahmad al-Hajji, an independent anti-regime activist, was among those killed yesterday.
Activists distributed a recording of Hajji taking part in a discussion on Syria that had been broadcast live on an official television channel months into the country's anti-Assad revolt.
Syria's war broke out after Assad's regime unleashed a brutal crackdown against dissent, when an Arab Spring-style revolt erupted, calling for change.