The Islamic State released hundreds of civilians used as human shields, as they fled in defeat from the northern Syrian city of Manbij on Friday. But the whereabouts other hostages remain unknown.

The fleeing fighters captured around 2,000 civilians to ward off air strikes as they headed towards the ISIL-held town of Jarabulus in cars.

According to the Syrian Observatory for Human Rights, the battle for Manbij which began in May has killed more than 400 civilians. Around three-hundred rebel fighters have been killed, along with more than a thousand jihadists.

On a separate front, government forces and rebels also clashed in the city of Aleppo on Saturday, leaving at least 51 civilians dead.