Syrian forces breach wall of Raqa’s Old City

US-backed forces in Syria have breached the wall surrounding the Old City of Raqa as they try to retake the city from the Islamic State group, the US Central Command said Monday night.

Centcom said in a statement that the coalition helped the advance of the Syrian Democratic Forces (SDF) by firing on two sections of the historic Rafiqah Wall.

"Coalition forces supported the SDF advance into the most heavily fortified portion of Raqa by opening two small gaps in the Rafiqah Wall that surrounds the Old City," it said.

US-backed fighters pierced jihadist-held Raqa from the south for the first time on Sunday, crossing the Euphrates River to enter a new part of the Syrian city, a monitor said.

The Syrian Democratic Forces have spent months closing in on the ISIS bastion and entered the city's east and west for the first time last month.

The city is an important hub for the group's operations, with ISIS having seized Raqqa in 2014, proclaiming it the capital of a "caliphate. The city became infamous as the scene of some of the group's worst atrocities, including public beheadings, and is thought to have been a hub for planning attacks overseas. It is reportedly defended by up to 4,000 fighters.

Centcom said the SDF faced heavy resistance at the wall from ISIS fighters who used it as a combat position and planted mines and improvised explosive devices against advancing US-backed soldiers.

"Conducting targeted strikes on two small portions of the wall allowed coalition and partner forces to breach the Old City at a locations of their choosing, denied ISIS the ability to use pre-positioned mines, IED and VBIEDs, protected SDF and civilian lives, and preserved the integrity of the greatest portion of the wall," the US statement said.

"The portions targeted were 25-meter sections and will help preserve the remainder of the overall 2,500-meter wall," it added.

The United Nations has expressed concern for up to 100,000 civilians it says are still trapped in the city, adding that at least 173 were killed in June, but that the actual figure could be far higher. It stressed that "civilians must not be sacrificed for the sake of rapid military victories".