The U.S. military maintains a small force of around 2,000 troops in northeastern Syria, where they have been helping the Kurdish-led SDF battle the Islamic State. An offensive for the last sliver of territory controlled by the militants in southeastern Syria was launched in September, but the Islamic State has put up a tough fight, and the battle has progressed more slowly than expected.

U.S. military officials estimate there are still around 2,000 Islamic State fighters holding out in the area, around the town of Hajin, and that there could be many thousands more sympathizers and supporters preparing to regroup in cells elsewhere.

Bombings claimed by the Islamic State have been on the rise in recent months, including one Wednesday in Raqqa, the group’s former de facto capital. That attack came as Trump tweeted that the militants had been defeated and that U.S. troops would be pulled out.