The leading US commander for the Middle East visited northern Syria on Saturday, officials said.
General Joseph Votel, head of US Central Command (Centcom), met with US military advisors working with Syrian Arab fighters and with leaders of the Syrian Democratic Forces, a Centcom spokesman said, declining to provide more details.
During the secret trip which lasted several hours, the Centcom commander visited a handful of locations, CNN reported as it accompanied Votel, the highest-ranking US military official to travel to Syria since its civil conflict began in 2011.
US special operations forces are helping train fighters in Syria to fight the Islamic State (IS) group as the United States leads a coalition of countries in an air war against the jihadists in Iraq and Syria.
IS has seized swathes of territory in Syria and Iraq to create a self-styled "caliphate." Its leader, Abu Bakr al-Baghdadi, has received pledges of alliance from jihadist groups around the world.