US-backed Syrian forces advancing against IS in Raqqa

US-backed forces seized a new neighbourhood from the Islamic State group in Raqqa, northern Syria, the group said on Monday.

The Syrian Democratic Forces - an alliance of Kurdish and Arab fighters - have been pressing an operation to capture the jihadi stronghold since last year, and they penetrated the city in June.

"The al-Yarmouk district was liberated yesterday," the SDF's spokeswoman for the Raqqa operation Jihan Sheikh Ahmed told AFP.

Yarmouk is a large neighbourhood on the south-western outskirts of the city.

"The operation is continuing but there are many fierce clashes," Ahmed said, speaking in the town of Ain al-Issa, 50 kilometres north of Raqqa.

"We are taking steady and sound steps. What is important to us is not speed, but liberating civilians and eliminating Daesh [IS]," she added.

An AFP reporter in Jazra suburb on the western outskirts of the city on Monday saw US-led coalition forces at a joint position with SDF fighters firing artillery in the direction of IS posts deeper inside Raqqa.

Progress inside Raqqa has been hampered by extensive mining of neighbourhoods, which has slowed advancing SDF fighters and also had devastating consequences for civilians trying to flee.

"There have been many casualties, fighters and civilians, caused by mines," an SDF commander told AFP, without giving his name.

"Yesterday, we buried six civilians after a mine exploded as they were trying to escape," he added.

The UK-based Syrian Observatory for Human Rights said the SDF had advanced in al-Yarmouk but did not yet fully control the district.

The monitor said the militia held the western portion of the district but that heavy fighting was continuing.

It also reported that hundreds of civilians had fled IS-held parts of the city towards areas now controlled by the SDF in the past 48-hours.

The SDF on its social media accounts said Monday its forces "managed to free about 500 civilians who were trapped inside the al-Daraiya and al-Tayar neighbourhoods, as well as 150 others from the Old City" inside Raqqa.

The monitor's Director Rami Abdel Rahman said a steady stream of civilians was fleeing IS-held districts.

"Whenever there is a lull in the fighting, they leave towards areas held by the SDF," he said.

The Syria Observatory estimates the US-backed force currently holds around 35 percent of the city.

The SDF began an operation to capture Raqqa in November 2016 and spent months taking territory around the city before finally entering it.

It has been backed by heavy US-led coalition air raids, including several on Monday that killed at least three civilians, according to the Observatory.

More than 330,000 people have been killed in Syria since the conflict began with anti-regime protests in March 2011.