US-backed fighters have seized a key ISIL stronghold in northern Syria after two months of heavy fighting and freed hundreds of civilians the extremists had used as human shields.

The town of Manbij “is under full control,” said Nasser Haj Mansour, of the predominantly Kurdish Syria Democratic Forces, adding that operations are continuing to search for any ISIL militants who might have stayed behind.

The SDF launched its offensive in late May to capture Manbij under the cover of US-led air strikes. The town lies on a key supply route between the Turkish border and the city of Raqqa, ISIL’s main stronghold in Syria.

Amateur videos showed that shortly after SDF fighters captured the town late on Friday, scores of residents went out to celebrate in the streets. Some men were seen clipping their beards with scissors while women were able to uncover their faces.

“May God destroy them. They slaughtered us,” a young man shouted in a Manbij square. “May they not live for a minute.”

In a photo posted online by Kurdish activists, a young woman defiantly uncovered her face while smoking a cigarette and flashing a victory sign.

Under the extremists’ reign, women had to wear long black cloaks that covered all but their eyes, while all adult men were forced to grow beards. Smoking was banned.

Mr Haj Mansour said some ISIL fighters were captured in the town while others fled to nearby villages.

“Military operations will continue until these villages are clean,” Mr Haj Mansour said.

Sherfan Darwish, another SDF official in Manbij, also confirmed that the town is under the full control of his fighters.

The capture of Manbij is the biggest defeat for the extremist group in Syria since July 2015, when they lost the town of Tal Abyad on the border with Turkey.

The Syrian Observatory for Human Rights said that with the capture of Manbij, hundreds of civilians that ISIL used as human shields are now free.

The extremists took around 2,000 civilians, including women and children, on Friday to ward off air strikes as they headed to the ISIL-held frontier town of Jarabulus, according to the SDF.

SDF fighters have been slowly advancing in the town and nearby villages over the past weeks. The fighting and the air strikes have killed 437 civilians, including more than 100 children, according to the Observatory. Around 300 SDF fighters died, along with more than 1,000 extremists, it said.

“The battle was very hard,” a Kurdish source said, adding that ISIL had laid mines in the city.

“One SDF fighter entered a house on Friday and saw a shoe placed on a Quran. When he removed it there was an explosion and he was killed,” the source said.

Pentagon deputy press secretary Gordon Trowbridge said ISIL “is clearly on the ropes”.

Since the battle for Manbij began, air strikes have destroyed more than 50 ISIL heavy weapons and more than 600 fortified fighting positions.

But the job of clearing the city will be difficult after the extremists left behind hundreds of mines and booby traps, Mr Trowbridge added.

ISIL has suffered major defeats over the past months in Syria and Iraq, where the military recaptured the cities of Ramadi and Fallujah in the western Anbar province. However, ISIL still controls large parts of Syria as well as Iraq’s second largest city, Mosul.