Fourteen civilians -- four of them children -- were killed when a barrage of barrel bombs hit the town of Al-Houla and neighbouring villages, according to the Syrian Observatory for Human Rights.
Barrel bombs are indiscriminate weapons typically dropped from helicopters. Their use in Syria's war has come under fierce criticism by rights groups but the regime denies using them.
Seven civilians, three of them children, were also killed on Thursday in government air strikes on the besieged town of Rastan, Observatory head Rami Abdel Rahman said.
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Rastan is one of the last rebel strongholds in the central province of Homs, and the town has suffered a devastating government siege since 2012 as well as deadly regime attacks in recent weeks.
On Wednesday, 13 member of the same family, including eight children, were killed there in regime bombardment.
The Observatory relies on a network of sources inside Syria to gather its information on the five-year-old conflict, which has killed more than 270,000 people and displaced millions.
It says it determines whether strikes were carried out by Syrian, Russian or US-led coalition aircraft based on the location of the raids, flight patterns and the types of planes and munitions involved.