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 the Britain-based group said 17 had been killed in the strikes.