US-led forces hit Islamic State bases in eastern Syria on Friday and a monitoring group said the Syrian army had intensified its bombing campaign in the west.
US and Arab forces began bombing Islamic State militants in northern and eastern Syria on Tuesday, prompting concern among Western-backed opponents of Syrian President Bashar Assad that the air campaign could play into his hands.
On Friday US Central Command, which has also been bombing bases of the al-Qaida splinter group in Iraq since last month, said it had destroyed more than a dozen Islamic State vehicles in both countries in its latest round of strikes.
The Britain-based Syrian Observatory for Human Rights, which monitors the conflict through a network of sources, said the Syrian army targeted areas held by a variety of insurgent groups, including Western-backed rebels.
Syrian warplanes used projectiles, including barrel bombs, in Hama, Idlib, Homs and Aleppo provinces and around Damascus, the Observatory said.
Five people were killed when barrel bombs were dropped on al-Rastan city in the Homs province and nine died in a barrel bomb attack east of Aleppo city, it said.