NORTHERN SYRIA -- American-backed Syrian militiamen who are fighting Islamic State of Iraq and Syria (ISIS) in Raqqa tell CBS News correspondent Holly Williams and her team they are just days away from declaring victory. ISIS militants seized Raqqa in 2014 and made it their de facto capital.

The drive to the frontline in Raqqa is at breakneck speed in a battered Humvee because ISIS snipers still lurk in the broken-down city, reports Williams, who is the only U.S. network correspondent to make it inside Raqqa during the offensive. ISIS fighters are holed up in what used to be Raqqa's main hospital.

They spot movement, and U.S.-backed militiamen open fire. But fighting there has been sporadic for days because they don't want to destroy what's left of the hospital – and because ISIS has human shields.

In the skeleton of a city, decimated by months of fighting and U.S. airstrikes, it's thought 2,000 civilians are still trapped.

Mike Hogan is from Phoenix, Arizona, and worked as a waiter before he volunteered to fight with the Syria militia men. He told Williams how one of his comrades fell to ISIS.

"He got shot by a sniper, through his wrist, and into his chest," Hogan said.

"He died right in front of you?" Williams asked.

"Yeah," Hogan responded, adding, "He spent two hours lying there while we tried to stabilize him. The ambulance that arrived to take him out arrived 20 minutes after he keeled over."

In a camp north of Raqqa, one squalid corner is reserved for the wives of ISIS fighters and their children. Their husbands have disappeared or are now in prison.

Mohammad Ramadan,13, told us ISIS trained him to use weapons and exposed him to horror.

"They brought a man in a car and tied him up for three hours," he told us, "then they cut off his head, and put it on top of a fence."

The people of Raqqa will rebuild, and the stench of death, which is everywhere in the city, will disappear. But its people will be haunted for a very long time to come.