The jihadists have set up barricades and minefields around the city and covered major roads in large sheets of cloth to make it more difficult for the US-led coalition to carry out airstrikes. Civilian men inside the city have been ordered to wear baggy trousers and long shirts to make it more difficult for SDF troops to distinguish them from jihadist fighters.

Many foreign fighters from the UK and other countries fled Raqqa ahead of the assault and relocated to Deir Ezzor province.

The US-led coalition is providing air cover for the SDF fighters as they advance and the Pentagon said 24 strikes had been launched in the past day. The Syrian Observatory for Human Rights said 21 people were killed in airstrikes on the north of the city on Monday.

Around 200,000 civilians are believed to still be inside the city and the International Rescue Committee, a global humanitarian group, said it was concerned Isil may use civilians as “human shields” against advancing troops.

“Given the large number of people still trapped in Raqqa it is essential the upmost care is taken to prevent further civilian causalities,” the group said.

Some civilians in the city were anxious that the SDF would drive out Isil only to hand control of Raqqa back to the Assad regime, according to Mohamad Kheder, an activist with the Sound and Picture Group. "To the civilians its like yellow Isil forces [SDF] are fighting with black Isil forces,” he said.