BEIRUT // ISIL launched a surprise assault near a besieged stronghold in northern Syria on Monday, killing residents of two villages it recaptured from US-backed fighters, a monitor said.

The Syrian Observatory for Human Rights said ISIL dispatched a small group of fighters – including one driving an explosives-laden car – into villages south-east of their bastion of Manbij.

The villages had been seized in recent weeks by the US-backed Syrian Democratic Forces in their push to take the town.

“ISIL is trying to defend Manbij by sending fighters from outside the town to attack the SDF in these villages,” said Rami Abdel Rahman, the director of the Britain-based Observatory.

“Daesh executed residents,” he added.

The US-led coalition backing the SDF carried out a barrage of air strikes to defend the villages, Mr Abdel Rahman said.

The clashes killed five SDF fighters and coalition air strikes left 42 extremists militants dead.

The SDF – a Kurdish-Arab alliance with air support from the coalition – encircled Manbij nearly 10 days ago.

Since then, they have been slowed by almost daily suicide bombings as ISIL puts up a fight for the town.

Held by the extremists since 2014, Manbij was a key stop along ISIL’s supply route from the Turkish border south-east through the town of Tabqa and on to its de facto Syrian capital of Raqqa.

ISIL is also mounting a fierce defence of Tabqa, which has been under attack by Russian-backed regime forces since early June.

On Monday, a failed ISIL counterattack against regime fighters south-west of Tabqa killed at least 14 extremists and six government loyalists, the Observatory said.

“ISIL dispatched 300 fighters from Raqqa to Tabqa to help defend the town,” Mr Abdel Rahman said.

The militants launched a second counterattack in the afternoon, seizing many positions south-west of the town and pushing pro-regime fighters about 20 kilometres back from Tabqa airport.

ISIL has lost 21 fighters since it began its assault on the region on Sunday, while 32 government loyalists have also been killed, according to the Observatory.

* Agence France-Presse