Barrel bomb attacks by Syrian regime helicopters killed at least 21 civilians late Thursday in a rebel-held town near Daraa city, a monitoring group said.
The Syrian Observatory for Human Rights said regime helicopters "dropped barrel bombs on neighbourhoods in Busra al-Sham in Daraa province," killing at least 21 people, including two children and four women.
Earlier, Observatory head Rami Abdel Rahman said the strikes had killed 17 people in the town in southern Syria.
Rebel groups seized full control of Busra al-Sham, an ancient town with both Sunni and Shiite Muslim residents, in March.
It was a major setback for forces loyal to embattled Syrian President Bashar al-Assad in the province where protesters first rose up against his rule in March 2011.
Assad's forces waged a bloody crackdown on the demonstrations, before people took up arms, leading to a full-blown war.
Since then, more than 240,000 people have been killed and millions have been forced to flee their homes.