A double bomb attack Tuesday (April 9th) in the northern Syrian city of al-Raqa, a former bastion of the "Islamic State of Iraq and Syria" (ISIS), killed 13 people, mostly civilians, AFP reported.

A car bomb and explosive ordnance struck a crowded street, killing nine civilians and four Syrian Democratic Forces (SDF) fighters, the Syrian Observatory for Human Rights said.

There was no immediate claim of responsibility for the attack near an SDF military outpost.

An al-Raqa resident said he saw black smoke rising above the site of the attack as ambulance sirens rang out.

He said he saw "blotches of blood on the ground".

"There is panic and fear in the area after the bombings," he added.

Al-Raqa city was captured by the SDF in 2017 after a massive operation against the extremists.

Earlier on Tuesday, a car bomb targeted a patrol of the international coalition in the north-eastern town of al-Shaddadi, the Observatory said.

But it failed to hit its target, leading only to the death of the suicide bomber, it said.

The SDF has warned that a new phase has begun in anti-ISIS operations, following the defeat of a proto-state the group had proclaimed in 2014.

They appealed for sustained coalition assistance to help smash sleeper cells.