US-backed militias say they have launched their final assault on Syria’s Raqqa on after a convoy of Islamic State fighters left the city, leaving only a hardcore of jihadists to mount a last stand.

“The battle will continue until the whole city is clean,” said a statement by the Syrian Democratic Forces (SDF), a US-backed alliance of Kurdish and Arab militias.

SDF spokesman Talal Selo told Reuters that 275 Syrian Islamic State fighters had withdrawn from the city along with civilian family members, leaving “no more than 200-300” foreign militants to fight on.

Under the terms of their withdrawal, all other civilians left in Raqqa were to be allowed safe passage out of the city, Selo said, adding that he believed only a few remained.

Raqqa’s fall to the SDF now looks imminent after four months of battle.

“We still expect there to be difficult fighting,” said Colonel Ryan Dillon, spokesman for the US-led international coalition backing the SDF in the war against Islamic State.

New officers of Syrian Democratic Forces take part during a graduation ceremony at a military camp in Ain Issa, Syria October 10, 2017. (Photo: Reuters)

Raqqa was the first big Syrian city to fall to Islamic State as it declared a “caliphate” and rampaged through Syria and Iraq in 2014, becoming an operations centre for attacks abroad and the stage for some of its darkest atrocities.

But Islamic State has been in retreat for two years, losing swathes of territory in both countries and forced back into an ever-diminishing foothold along the Euphrates river valley.

“Last night, the final batch of fighters (who had agreed to leave) left the city,” said Mostafa Bali, another SDF spokesman.

There were conflicting accounts as to how many people left in the convoy and who they were.

Selo said 275 Syrian fighters left along with their family members. Laila Mostafa, head of the Raqqa Civil Council, formed under SDF auspices to oversee the city, said that figure included both the fighters and their family members. She said an earlier comment by another council member that some foreign fighters had left in the convoy was wrong.

Before the convoy left, the coalition estimated that about 300-400 fighters remained.

Reuters