US-backed forces to launch battle for IS capital Raqqa in a 'few days'

A US-backed Kurdish-Arab Alliance has seized new territory west of the Islamic State group's Syrian bastion of Raqqa, as its operation to take control of the city is set to begin in a "few days," a spokesman from the YPG militia said. 

"The forces reached the outskirts of the city, and the major operation will start ... in the coming few days," YPG spokesman Nouri Mahmoud told Reuters by phone.

The Britain-based Syrian Observatory for Human Rights monitor said the SDF captured the town of Mansura late on Friday and the adjacent Baath Dam on the Euphrates River, around 20km west of Raqqa, on Saturday.

SDF spokesman Talal Sello confirmed the force was advancing on the western front without providing details.

"This advance will allow the SDF to expand its control on the southern banks of the Euphrates River and stabilise the western front of Raqqa before launching the final battle to expel IS from the city," Observatory director Rami Abdel Rahman said.

"We're nearing the major battle," he added.

Abdel Rahman said combing operations were continuing in Mansura and at the dam to "dismantle mines and search for remaining jihadists".

Sello told AFP the advances on the western front were part of the final stage of operations before the launch of the assault on Raqqa itself.

He said the SDF had received "weapons and advanced equipment from the international coalition ... as part of preparations for the launch of the battle for Raqqa, which is close".

Sello said the SDF would launch the attack from the north, west and east of Raqqa.

"The SDF has already completed the siege from the northern and eastern sides and is working to complete the siege from the west," he said.

The SDF is fighting with broad support from the US-led coalition, which has provided air cover, assistance from special forces on the ground, and weaponry.

SDF fighters are now just a few kilometres from the city on the north, east and western fronts, with all major routes into the city severed.

IS fighters are still able to move out of the city to the south, however, crossing the Euphrates by boat before continuing on through the desert.

The SDF is not expected to try to seal the southern route before launching its final assault.

"The SDF doesn't need to isolate Raqqa from the south because the international coalition's planes can target any jihadists as they cross the river," Abdel Rahman said.