The Syrian Kurdish YPG militia says Isis is on the verge of defeat in Raqqa, and the city may be finally cleared of jihadists on Saturday or Sunday.

"The battles are continuing in Raqqa city. Daesh (Isis) is on the verge of being finished. Today or tomorrow the city may be liberated," YPG spokesman Nouri Mahmoud said.

The YPG dominates the US-backed Syrian Democratic Forces (SDF), an alliance of Arab and Kurdish militias that has been battling since June to defeat Isis at Raqqa, which served as the jihadist group's de facto capital in Syria.

An activist group that reports on Raqqa, Raqqa Is Being Slaughtered Silently, said on its Facebook page on Saturday that dozens of buses had entered Raqqa city overnight, having travelled from the northern Raqqa countryside.

The Britain-based Observatory said Syrian Isis fighters and their families had already left the city, and buses had arrived to evacuate remaining foreign fighters and their families. It did not say where they would be taken to.

The Observatory said the evacuation was taking place according to a deal reached between the SDF and the US-led coalition on the one hand, and Isis on the other.

The US-led coalition and SDF officials could not immediately be reached for comment on the Observatory report.

During the more than six-year Syrian war, the arrival of buses in a conflict zone has often signalled an evacuation of combatants and civilians.

In August, Isis fighters agreed to be evacuated from a Lebanon-Syria border area, the first time the militants had publicly agreed to a forced evacuation from territory they held in Syria.

In pictures: Muslims in London protest against Isis Show all 7 1 /7 In pictures: Muslims in London protest against Isis In pictures: Muslims in London protest against Isis Muslims gather with flags in Trafalgar Square on October 1, 2017 Getty In pictures: Muslims in London protest against Isis People listen to a speaker in Trafalgar Square on October 1, 2017 Getty In pictures: Muslims in London protest against Isis Protesters gather with placards ahead of the annual Ashura march in Marble Arch on October 1, 2017 Getty In pictures: Muslims in London protest against Isis Muslims pray ahead of the annual Ashura march in Marble Arch on October 1, 2017 Getty In pictures: Muslims in London protest against Isis Protesters holding placards demonstrate along Oxford Street on October 1, 2017 Getty In pictures: Muslims in London protest against Isis Protesters gather with placards during the annual Ashura march in Marble Arch on October 1, 2017 Getty In pictures: Muslims in London protest against Isis Protesters holding flags and placards demonstrate along Oxford Street on October 1, 2017 Getty

Civilians have been making perilous journeys to escape Isis-held areas as SDF forces advance. The SDF says it helps transport them away from the fighting after they flee.

The offensive to drive Isis out of Raqqa, its de facto Syrian capital which it seized in 2014, has long outlasted initial predictions by SDF officials who said ahead of a final assault in June that it could take just weeks.

The US-led coalition could not immediately be reached for comment.