The US-backed Syrian Democratic Forces has started a ground operation to clear the last ISIS enclave in Syria, a spokesman for the group told CNN Friday.

SDF spokesman Mustafa Bali said thousands of civilians have been evacuated and kidnapped fighters have been freed in Baghouz, in eastern Syria,

“Only the terrorists remain in Baghouz.” Bali said in a tweet.

At its height, ISIS controlled huge swaths of territory in Syria and Iraq. A US-led coalition has been working for years to oust the group from cities and towns.

One soldier in Baghouz during the evacuation of civilians told CNN that the wives of ISIS martyrs are there with their children and they don’t want to leave. Multiple US officials told CNN’s Barbara Starr that civilians still remain in the last piece of territory remaining under ISIS control.

David Eubank, director of the Free Burma Rangers, a Christian humanitarian group that operates in the area,estimates that in the last month, around 15,000 people have fled Baghouz.

The SDF launched an offensive last month to oust ISIS from the enclave.

Before the offensive started, SDF officials estimated that 1,500 civilians and 500 ISIS fighters remained, but as the assault got under way it became clear that the actual number was much higher.

The militants include some of the most battle-hardened and experienced personnel remaining in ISIS. Some of those being used as human shields are the wives and children of those ISIS fighters.

On Thursday, President Donald Trump said that US-backed forces have retaken 100% of the territory once claimed by ISIS in Syria. That announcement surprised US officials and regional allies leading the fight who told CNN the battle isn’t over. An SDF officer said the group was surprised by the statement and said fighting has been ongoing.