Raqqa, Syria (CNN) CNN has gained rare access inside the Old City of Raqqa, as rebels and international forces tightened their circle around ISIS' de facto capital.

US-led airstrikes breached the 1,300-year-old Rafiqah Wall on Monday and allowed the US-backed Syrian Democratic Forces (SDF) to enter the city from the south. CNN is the first Western media organization to film inside the fortification since then.

After pushing through one of two small gaps in the wall, CNN journalists met with the rebels leading the assault just 200 meters from ISIS positions, as they heard gunfire and explosions nearby.

The rebels have seized control of territory around 300 meters into the Old City since Monday, but have been confronted with fierce resistance from ISIS.

CNN saw US forces in this area and it appears they have been calling in the airstrikes that have cleared the way for the rebels' advances. US personnel did not want to be filmed.

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