AMMAN: Islamic State claimed responsibility for suicide and car bomb blasts that struck a Damascus suburb on Saturday near Syria's holiest Muslim shrine, and a monitoring group said at least 20 people were killed.

State television showed debris, mangled cars and wrecked shops in a main commercial thoroughfare near the Sayeda Zeinab shrine, in an area where at least three bomb attacks claimed by Islamic State have killed and wounded scores of people this year.

State media said at least eight people were killed. But the UK-based Syrian Observatory for Human Rights said the death toll had risen to at least 20, including at least 13 civilians, with the other victims coming from pro-government militias.

It said the number was expected to rise because many of the scores of wounded people were in critical condition.

Islamic State said two of its suicide bombers had blown themselves up and operatives had detonated an explosives-laden car, according to the IS-affiliated Amaq news agency.

The Sayeda Zeinab shrine is a magnet for thousands of Iraqi and Afghan militia recruits who go there before being assigned to front lines, where they fight against the Sunni rebel groups trying to topple President Bashar al-Assad.

Almost every militia fighter bears insignia on his combat fatigues with the words “For your sake, Sayeda Zeinab”.

Sectarian split

The heavily garrisoned area near the shrine is also a well known stronghold of Lebanon's powerful Hezbollah group, an Iranian-backed movement that is one of Assad's chief allies.

Rebels say Iran's strong military intervention on the side of Assad, alongside its backing of other militias, is fuelling the sectarian dimension of the nearly six-year Syrian civil war by drawing even more radical foreign militants into the country.

Separately, US-backed Syrian forces made new territorial gains against Islamic State on Saturday, moving closer to another of its major strongholds in northern Syria, according to the monitoring group.

The Observatory said the Syria Democratic Forces (SDF), bringing together Kurdish and Arab fighters, were now almost 17 km from the city of al-Bab, an Islamic State stronghold north east of Aleppo.

The SDF on Friday cut off the last route into the encircled town of Manbij from al-Bab after over a week of advances around that area, allowing it to lay siege to the large town from all directions, the monitor said.

In other frontlines in northern Syria, two rebel sources said Russian and Syrian jets stepped up their relentless aerial bombing of their positions in the northern city of Aleppo.