Damascus, Jul 4 (IANS): The Washington-backed Syrian Democratic Forces (SDF) breached a wall surrounding the Old City of Raqqa, the last bastion of the Islamic State (IS) terror group, the US Central Command (CENTCOM) said in a statement.

IS fighters were using the historic Rafiqah Wall as a fighting position and had planted mines and improvised explosive devices at several breaks in the wall, the CENTCOM statement said late Monday.

"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," CNN quoted the statement as saying.

The Rafiqah Wall surrounds the Old City of Raqqa in the southeastern part of the city, according to Syrian state media.

The wall is approximately 5 km long, 3.8 metres high and 1 metre thick. It is approximately 3 km away from the city centre.

"The portions targeted were 25-metre sections and will help preserve the remainder of the overall 2,500-metre wall," the statement said.

CENTCOM and the SDF did not specify which area of the wall was breached, reports CNN.

The US envoy for the anti-IS coalition, Brett McGurk, said Monday's operation by the SDF was "a key milestone in the campaign to liberate the city".

The SDF launched an offensive to seize Raqqa on June 6.

For over three years, IS has used the city as a staging ground for its deadly attacks in the Middle East and further overseas.