BEIRUT - At least 20 people, including four children, were killed Sunday in a second day of deadly air strikes on Al-Bab in northern Syria, said the Syrian Observatory for Human Rights.
The Britain-based monitoring group said they were killed when regime helicopters dropped explosives-laden barrels on a market area of Al-Bab, a day after similar attacks killed at least 26 others in the same town.
"The toll is likely to rise as dozens were wounded, some of them critically, and there are reports of victims trapped under the rubble," said the Observatory.
The Syrian regime has regularly been accused by the opposition, foreign governments and rights groups of using so-called "barrel bombs" against civilians.
The US State Department has described the weapons as "incendiary bombs which contain flammable material that can be like napalm."
Elsewhere, the Observatory said at least five regime forces were killed overnight in a suicide car bomb attack at a police checkpoint on the Damascus-Homs highway near the contested town of Nabuk.
The group said a fighter from the jihadist Al-Nusra Front carried out the attack, which came as regime forces try to gain control of Nabuk, as part of an operation to recapture the Qalamoun region.
The army has already captured the towns of Qara and Deir Attiyeh, and a Syrian security source told AFP troops now controlled 60 per cent of Nabuk, which lies further south towards the capital on the Damascus-Homs highway.
The Observatory said regime warplanes carried out air strikes on the town on Sunday, and fierce fighting continued there between rebel fighters, including jihadists, and army troops backed by a pro-regime militia and Lebanon's Shiite Hezbollah.
The Syrian regime is trying to sever rebel supply routes that run through the mountainous Qalamoun region, north of Damascus, across the nearby border with Lebanon. The fighting has spread to nearby Maalula, a Christian town, that was attacked by rebel fighters in September.
Regime troops had succeeded in recapturing the centre of the town, but rebels renewed their attacks there over the weekend "in an attempt to lessen the pressure on the terrorists encircled in Nabuk," a Syrian security source said.
In Eastern Ghouta east of Damascus, fighting pitting rebels against troops raged on, days after opposition fighters including jihadists launched a bid to break a year-long siege there.
Five rebel fighters were killed in battles there Sunday, said the Observatory.