CNN's Nick Paton Walsh reports from inside the encircled Old City of Raqqa, offering rare insight into the battle to retake the capital of ISIS's self-declared caliphate.



The terrorist group is preparing to make its "final stand," he reported. "We've seen U.S. forces here, not far from these positions, anxious not to be filmed or even noticed, frankly, but we understand it is them, calling in the air strikes and artillery that are allowing these forces to move forward so quickly."



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The area held by ISIS is "increasingly small," he reported. Potentially as small as "one and a half to three miles" across.



"This marks potentially the last time I'll be able to say ISIS holds a city in Syria," Paton Walsh said.





NICK PATON WALSH: We are now inside the Old City Walls of Raqqa,

the capitol of ISIS's self-declared Caliphate of terrirory, at which they will make their final stand in Syria, and really in the Middle East.



That wall is a key milestone for coalition forces, and for the Syrian Kurds, who now control roughtly 200-300 meters inside the Old City. Down that way 200 meters are ISIS's positions. The forces here don't move around much in the daylight because of the threat of ISIS snipers, but it is at night when the majority of the movement forward takes place.



We've seen U.S. forces here, not far from these positions, anxious not to be filmed or even noticed, frankly, but we understand it is them, calling in the air strikes and artillery that are allowing these forces to move forward so quickly.



I've been surprised how little of the city ISIS are apparently in right now, and area possibly one and a half to three miles in terms of size. Increasingly small, the terrain that they hold. But as we saw in Iraq, civilians apparently held in their midst, unable to flee because of the ISIS snipers. A real impedement for these Kurdish, Syrian, and Arab fighters.



There is progress here, marking potentially the last time that I'll be able say ISIS holds a city in Syria.

