The top U.S. commander for the Middle East has secretly visited Syria for a first-hand look at efforts to build cohesive alliances of Arab, Kurd and other local fighters to defeat the Islamic State.

Army Gen. Joseph Votel, who is head of U.S. Central Command, flew into northern Syria on Saturday and spent nearly 11 hours in the country. He met with U.S. military advisers working with Syrian Arab fighters, and conferred with leaders of the Syrian Democratic Forces. That's an umbrella group of Kurdish and Arab fighters supported by the U.S.

Votel was the highest-ranking U.S. military officer known to have entered Syria since the U.S. began its campaign to counter the Islamic State in 2014.