At least 15 people have been killed and many more wounded by two bomb blasts in the rebel-held Syrian city of Idlib.

Key points: Many casualties were emergency workers who rushed to help victims of the first blast

Many casualties were emergency workers who rushed to help victims of the first blast Idlib has seen an escalation in artillery fire from the Syrian army

Idlib has seen an escalation in artillery fire from the Syrian army Commander of US-backed forces called for 1,500 international soldiers to remain in Syria

Many of the casualties are reported to be emergency workers who rushed to the scene after the first explosion.

Idlib province, in Syria's northwest corner, is under the control of Hayat Tahrir Al Sham, a bloc of Islamist militant factions spearheaded by Syria's former Al Qaeda affiliate, and has long been targeted by bombings and assassinations.

Video posted to social media purports to show the aftermath of the fatal twin explosions.

Medics and witnesses said scores were injured.

They said an explosive device planted in a parked car detonated in a main street, and the second blast was attributed by some witnesses to a bomb rigged to a motorcycle.

Syrian Civil Defence members, known as White Helmets, were seen carrying away bodies and rescuing wounded civilians amid smouldering wreckage.

Alliance commanders said hundreds of people had been rounded up for suspected links to Syrian President Bashar al-Assad's intelligence services or Islamic State sleeper cells who they blame for some of the bombings.

Idlib, which borders Turkey, has also seen an escalation in artillery fire from the Syrian army and allied Iranian-backed militias. ( AP: Felipe Dana )

They say the wave of blasts in the densely populated region, a haven for tens of thousands of civilians opposed to Mr Assad's rule, aims to destabilise the last remaining opposition bastion after almost eight years of civil war.

Idlib, which borders Turkey, has also seen an escalation in artillery fire from the Syrian army and allied Iranian-backed militias on rebel-held towns, witnesses said.

The latest fatalities come as the commander of US-backed forces in Syria called for about 1,000 to 1,500 international forces to remain in Syria to help fight Islamic State and expressed hope that the United States, in particular, would halt plans for a total pullout.

Reuters