Syrian warplanes bombed positions belonging to the jihadist Islamic State group in the northern province of Raqa for a second day on Monday, a monitoring group said.
On Sunday, regime planes killed 31 jihadists and eight civilians in an unprecedented wave of aerial bombardment against the group in its Raqa bastion.
The bombing continued on Monday, according to the Syrian Observatory for Human Rights, with at least 16 raids targeting jihadist positions.
It said three civilians were killed.
Three raids targeted the area around the town of Tabqa in western Raqa and four hit near the Tabqa military airport, the only remaining regime-held position in the province.
The other nine strikes hit sites inside Raqa city, the provincial capital.
The raids involved the use of precision weapons rather than the explosive-packed barrel bombs that the regime has deployed to deadly effect in Aleppo province and elsewhere.
Barrel bombs have been criticised for being indiscriminate and killing civilians.
In Aleppo province on Monday, warplanes targeted several IS-held positions, with eight civilians reported killed at Menbej.
In the eastern province of Deir Ezzor bordering Iraq, IS militants executed a woman dentist after accusing her of setting up a pro-regime espionage cell, the Observatory said.
It said she was abducted from her clinic at Mayadeen along with four friends, whose fate remains unknown.
The Syrian air raids come as the United States carries out air strikes against the Islamic State just across the border in neighbouring Iraq.
The US strikes are intended to limit the advance of IS militants who have seized large swathes of territory in both Iraq and Syria, declaring an Islamic "caliphate".
The group emerged from Al-Qaeda's one-time Iraq affiliate, but has since broken with that organisation and grown into a cross-border militant group.
It has been battling rival opposition fighters in Syria since early January, after a backlash because of the group's abuses against civilians and rebels, and its bid to dominate captured territory.