Transcript for Turkey moves military convoys and special forces to Syria border
Jon, thank you. Now, to fast-moving developments after president trump suddenly decided to pull out U.S. Troops from a key region of Syria, which would leave kurdish fighters defend for themselves against Turkey. Tonight, Turkish troops are already grothering at the Syrian border, refddy to move in. And this evening, the Turkish president has indicated an operation is imminent. He's also been invited to the white house. ABC's senior foernt correspondent Ian Pannell from istanbul. Reporter: Tonight, Turkey moving its war machines into place. Long convoys of military hardware up to the border with Syria. Setting the stage for a military invasion targeting the kurds. President trump now facing fierce backlash for pulling back American troops straight after a phone call with president of erdogan of Turkey. President trump accused of abandoning a key partner in the fight against ISIS. At some point, we have to bring our people back home. And that's what we're doing. Is it a firm decision, sir? It's always a firm decision. Reporter: The president standing by his decision, today insisting in a tweet, "In no way have we abandoned the kurds, who are special people and wonderful fighters. We are helping the kurds financially/weapons." But without the close protection from U.S. Troops at the border, kurdish forces are far more vulnerable to a much stronger Turkish army. For years, we've followed the kurds in their fight against ISIS, here battling street by street to liberate the city of raqqah. The U.S. Coalition is working with -- they are the foot soldiers, and we're moving up to their forward base. This kurdish woman was leading a band of soldiers, no body armor, no tanks or humvees. That very night, she was killed in battle, one of 11,000 kurds who paid the ultimate price defending their homeland and protecting America and Europe from ISIS. Tonight, more than 10,000 ISIS militants sit in Syrian prisons under the watch of kurdish guards. So, what happens if those kurds are forced to leave those prisons and fight the Turks? David on the ground asking about the threat of those fighters. There are reports, up to 10,000 ISIS fighters are being held by american-backed forces right now. What do you do with those fighters? It's a really good question, and it's a tough question. So, we've got to get the countries to take ownership of their folks who came here into the battlefield, take them back and figure out how to bring them to justice. Now even bigger questions about those fighters. Ian joins us. And as you pointed out there, one of the major concerns are the thousands of ISIS fighters being watched by our kurdish allies. Some of the prisoners there telling us, if they get out, they want to go after America. What's the concern on the ground there tonight? Reporter: Absolutely, David. A very real danger. And what makes out even worse is that the kurdish forces are now saying that if Turkey crosses over the border, then they're going to pull back their troops from the areas around the prison, other newly lib rated areas, to try to reinforce the front lines. And also this evening, the former head of American forces in the Middle East writing that president trump's decision threatens to undo five years worth of fighting against ISIS and also undermine America's credibility. David? A lot of moving parts on this, as well. Ian, thank you.
This transcript has been automatically generated and may not be 100% accurate.