MOSUL, Iraq -- A bulldozed mound of dirt and a short stretch of no man's land is all that separates Iraqi forces from Islamic State of Iraq and Syria (ISIS) militants.

As an Iraqi machine gunner opens fire, an armored personnel carrier rolls in to provide cover.

An Iraqi machine gunner fires toward an ISIS position in Mosul. CBS News

It's hard to tell if the troops were aiming at a specific target, or putting on a display for our benefit. But the response from ISIS was very real; A mortar was sent whizzing low over our heads and exploded in the rubble behind us.

Near the Old City, whole neighborhoods are flattened. The sheer level of destruction is staggering and it goes on for miles and miles. But it is one tactic the Iraqi Army cannot afford to employ in the Old City if they want anything left of it.

Whole neighborhoods in Mosul are flattened. CBS News

The UN estimates 200,000 Iraqi residents are still trapped inside, and those who try to escape risk being caught in crossfire.

We found 11-year-old Sarah at a hospital run by American medical volunteers, where Dr. John Lucey was treating her for a shrapnel wound.

Sarah, 11, was at a hospital run by American medical volunteers. CBS News

"This is right through her mid-foot," Lucey said.

The orthopedic surgeon from Ashville, North Carolina, came out of retirement at 74 years old to do what he could in Iraq as part of the organization Samaritan's Purse. He said he was shocked by what he saw.

"I came here, and probably the first two days I could almost not take it. I've seen a lot of trauma but I've never seen anything to this extent," he said.

Lucey says the hospital is ready for more patients in the coming weeks. Hopefully, that will mean more families trapped inside the Old City have at least escaped with their lives.