Transcript for Hundreds of ISIS fighters surrendering as US issues new warning

We turn overseas tonight, we have reported here on president trump wanting forces out of Syria. He does acknowledge that a small military footpoint is necessary. And tonight, look at these new images. Hundreds of ISIS fighters leaving the last territory they still hold in Syria. And this evening, a top U.S. Commander with a new warning. Here's ABC's senior foreign correspondent Ian Pannell tonight. Reporter: Tonight, hundreds of desperate and defeated ISIS fighters stumbling to surrender. Many of their families now huddled in makeshift camps, dirty and hungry. But many, still defiant. And tonight, with the level of U.S. Troops in Syria set to drop from 3,000 to 400, a new warning from the head of U.S. Central command. What we are seeing now is not the surrender of ISIS as an organization, but a calculated decision to preserve the safety of their families and preservation of their capabilities in going to ground and remote areas and waiting for the right time to resurge. Reporter: We've been covering the fight in Syria for years. You've got local forces backed by the United States taking the battle to ISIS militants. From a so-called caliphate that once stretched across large swaths of Syria and Iraq, what remains is the small village of baghouz, just one square mill. U.S. Commanders warning there could be 20,000 ISIS fighters still in Iraq, and that unless the U.S. And others come up with a plan, the seeds of extremism will continue to grow. David? Ian Pannell tonight. Thank you, Ian.

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