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.

Obama hails Syria arms destruction, vows vigilance
Washington (AFP) Aug 18, 2014 - US President Barack Obama hailed the completion Monday of the destruction of Syria's chemical weapon stockpile, but said Washington would seek to ensure that Damascus fulfills all its commitments.

"Today we mark an important achievement in our ongoing effort to counter the spread of weapons of mass destruction by eliminating Syria's declared chemical weapons stockpile," Obama said in a statement.

He said the destruction, carried out aboard a US Navy ship on the Mediterranean Sea, sent "a clear message that the use of these abhorrent weapons has consequences and will not be tolerated by the international community."

After a global outcry over deadly chemical attacks in a Damascus suburb last year that may have killed as many as 1,400 people, President Bashar al-Assad's regime agreed to an international plan to destroy its stockpile.

"Going forward, we will watch closely to see that Syria fulfills its commitment to destroy its remaining declared chemical weapons production facilities," Obama said.

US Secretary of State John Kerry reiterated that "much more work must be done" as he marked what he said was "a milestone in our unrelenting work to ensure the end of the Assad regime's deadly chemical arsenal."

"The United States will continue to provide political, financial and other support to the moderate opposition because we are committed to help those who seek the right of all Syrians to choose a future of peace and oppose the violent extremists who exploit the chaos and ruin that Assad has brought to Syria," Kerry said in a statement.

With no country ready to accept shipments of Syria's most lethal chemical agents, the United States proposed destroying the chemicals at sea using two "portable" hydrolysis units.

Defense Secretary Chuck Hagel called the captain of the MV Cape Ray earlier in the day to congratulate the crew on "their unprecedented work of neutralizing, at sea, the most dangerous chemicals in Syria's declared stockpile," the Pentagon said.

The process called for mixing the chemicals in sealed containers with thousands of gallons of hot water along with sodium hydroxide or other "reagents" that help break down their toxicity.

Officials have said none of the chemicals or waste will be dumped at sea.