An explosion struck near a patrol of the US-led coalition in the northern Syrian town of Manbij, killing and wounding more than a dozen people, a Syrian war monitoring group and a local town council said.

The Britain-based Syrian Observatory for Human Rights said 16 people were killed including nine civilians and others were wounded in the blast.

An Islamic State-affiliated website said the explosion was the work of a suicide bomber, and that at least five US-backed Syrian fighters were among the dead.

This comes as U.S. Vice President Mike Pence claimed that the Islamic State “caliphate has crumbled” and the militant network “has been defeated.”

His comments were made during in a speech at the State Department shortly after the explosion.

Mr Pence defended President Donald Trump’s decision to withdraw the 2,000 U.S. troops from Syria. Critics say the pullout is premature.

He says the withdrawal will be “orderly and effective” and that the U.S. will stay in the region to make sure IS does not regroup.

The rare attack came days after the US began the process of withdrawing from Syria, pulling out equipment from the northeast into neighbouring Iraq.

There was no immediate comment from the US-led coalition on whether there were casualties among coalition forces.

US military Colonel Sean Ryan said they were “aware of open source reports regarding an explosion in Syria.

“Coalition forces conducted a routine patrol in Syria today. We are still gathering information and will share additional details at a later time.”

Videos released by local activists and news agencies showed a restaurant that suffered extensive damage and a street covered with debris and blood.

Several cars were also damaged.

Another video showed a helicopter flying over the area.

The Kurdish Hawar news agency, based in northern Syria, and the Observatory, which monitors the war through activists on the ground, reported two US troops were among the casualties.

Turkey’s state-run Anadolu Agency, citing unnamed local sources, said a number of US soldiers were injured in the blast and that the US military evacuated soldiers by helicopter.

The Observatory and the Kurdish-led Manbij Military Council, which runs the town, said the blast occurred near a restaurant near the town’s main market.

The Observatory’s chief Rami Abdurahman also said the explosion was caused by a suicide bomber but didn’t immediately have any further details.

It was not the first time that forces of the US-led coalition were subjected to attacks in the area, although they have been rare.

In March last year, a roadside bomb killed two coalition personnel, an American and a Briton, and wounded five in Manbij.