(CNN)US-backed rebels have breached a strategic wall surrounding the Old City of Raqqa in ISIS's self-declared capital on Monday, US Central Command has said in a statement.
Raqqa: US-backed forces breach Old City's wall
Breaching the Rafiqah Wall means the Syrian Democratic Forces will be able to penetrate Raqqa's Old City, the last redoubt of ISIS defenders in the city. The ancient wall -- first constructed in the 8th century by the Abbasid dynasty and stretching around the Old City on three sides -- has provided important fortification for ISIS.
The operation was "a key milestone" in the campaign to "liberate the city," Brett McGurk, the US envoy for the anti-ISIS coalition, said on his official Twitter account.
In a CENTCOM statement, the US added: "Coalition forces supported the SDF advance into the most heavily fortified portion of Raqqa by opening two small gaps in the Rafiqah Wall that surrounds the Old City."
The battle for Raqqa is not dissimilar to that of Mosul, where US-backed Iraqi forces are fighting to expel the last of ISIS fighters from Iraq's second-largest city. But the fight to retake Raqqa has gone quicker, with attacking forces gradually forcing a diminishing number of ISIS fighters into a smaller area of narrow streets around the ancient mosque of Rafiqa, which has already been extensively damaged.
The Rafiqah Wall -- which is 3 kilometers from the city center -- is approximately 5 kilometers (3.1 miles) long, 3.8 meters (12.4 feet) high and 1 meter thick, Syrian state media reported in 2009.
ISIS fighters had planted mines and improvised explosive devices at several breaks in the wall, a US Central Command (CENTCOM) statement said.
"The portions targeted were 25-meter sections and will help preserve the remainder of the overall 2,500-meter wall," CENTCOM said.
CENTCOM and the SDF did not specify which area of the wall was breached.
The SDF launched an offensive to seize Raqqa on June 6. For more than three years, ISIS has used Raqqa as a staging ground for its deadly attacks on the Middle East and further overseas.
The group is running out of places to go. If ISIS is evicted from Raqqa it will lose the last vestige of any "governance" of its so-called caliphate. But it's not just losing control of territory, it will also lose the facility to move freely between Syria and Iraq -- especially since Iraqi militia seized the key town of Baaj last month.
The coalition hopes that the loss of Raqqa and Mosul will dull ISIS' appeal to potential recruits.
"It's hard to convince new recruits that ISIS is a winning cause when they just lost their twin 'capitals' in both Iraq and Syria," General Steve Townsend, the coalition's commanding general, said.