United States-backed forces in Syria have entered the most heavily fortified area of Raqqa, the de facto capital of Daesh (ISIS), in what a U.S. official says is a "key milestone" in the war against the extremist group.
Success in Raqqa and major advances by U.S.-backed forces in Mosul, a second Daesh stronghold in Iraq, represent a powerful double blow to the violent extremist group.
The U.S. Central Command said in a statement dated Tuesday that coalition forces supported an advance by Syrian Democratic Forces fighters "into the most heavily fortified portion of Raqqa by opening two small gaps in the Rafiqah Wall that surrounds the Old City."
The SDF faced heavy resistance, as the Daesh fighters used the wall as a combat position and planted mines and improvised explosive devices against advancing fighters.
"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," the statement read.
This prevented IS from using "pre-positioned mines, IED and VBIEDs, protected SDF and civilian lives, and preserved the integrity of the greatest portion of the wall."
A 25-meter section of the wall was targeted, which "will help preserve the remainder of the overall 2,500-meter wall," it added.
Brett McGurk, the U.S. special presidential envoy for the coalition to defeat Daesh, said on Twitter that breaching the wall in Raqqa was a "key milestone in campaign to liberate the city."
The U.S.-backed fighters entered Raqqa 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 SDF have spent months closing in on the Daesh bastion and entered the city's east and west for the first time last month.
According to the coalition, some 2,500 Daesh militants are defending the city.
Daesh overran Raqqa in 2014, turning it into the de facto capital of its self-declared "caliphate."
The city was the scene of some of the group's worst atrocities, including public beheadings.
The United Nations warn that up to 100,000 civilians are still trapped in the city.
McGurk earlier tweeted: "#ISIS terrorists down to less than one square kilometer in #Mosul and totally surrounded in #Raqqa, #SDF advancing from four directions."
In Mosul, Iraqi forces face stiff fighting and a rising number of suicide attacks, including some by female bombers, as they enter the final stages of the battle.
More than eight months since the start of the operation to retake Mosul, Daesh fighters have gone from fully controlling the northern Iraqi city to holding a limited area on its western side.
Iraqi forces have been closing in on the Old City in west Mosul for months, but the terrain combined with a large civilian population has made for an extremely difficult fight.
Daesh overran large areas in Iraq north and west of Baghdad in 2014, but Iraqi forces backed by U.S.-led coalition air strikes have since regained much of the territory they lost.
The Iraqi military believes that there are just a few hundred Daesh militants left in Mosul.