NORTHERN SYRIA -- Syrian forces backed by the U.S. military are beginning what's being called the final push to drive the Islamic State of Iraq and Syria (ISIS) out of Raqqa. The militant group has controlled the city for more than three years.

The U.S.-backed Syrian militia group that's leading the fight on the ground in Raqqa says victory is just days away.

ISIS is thought to have around 250 fighters left in the city -- and they are holed up in a handful of buildings including the main hospital and the sports stadium.

CBS News spent two days in Raqqa with those American-backed fighters and we saw the skeleton of a city -- block after block has been devastated by fighting, and by U.S. coalition airstrikes.

A U.S. special operations commander in Syria told CBS News on Sunday that around 2,000 civilians are still trapped and they are unable to escape the small area controlled by ISIS gunmen.

Raqqa was a place where ISIS reveled in its own brutality -- carrying out public beheadings -- and revealing its leaders to be bloodthirsty killers. It is a twisted version of Islam that is unrecognizable to most Muslims.

The loss of Raqqa is symbolic because it was the so-called ISIS capital - but along with the loss of other town and cities in Syria and Iraq, it may also weaken the group's ability to carry out terror attacks both here in the Middle East, and elsewhere.