The top U.S. commander for the Middle East secretly visited Syria on Saturday, May 21 officials said, according to BBC News.
General Joseph Votel, head of U.S. Central Command, spent about 11 hours in northern Syria.
He met U.S. military advisers and the leaders of the Syrian Democratic Forces (SDF), made up of Kurdish and Arab rebel forces.
The U.S. wants local forces to defeat the so-called Islamic State (IS) group, which holds territory in the country.
Speaking after the visit, Gen Votel said training local forces to fight IS was the right approach.
"I left with increased confidence in their capabilities and our ability to support them. I think that model is working and working well," he said.
The SDF comprises about 25,000 Kurdish fighters and about 5,000 Arab fighters. The U.S. is hoping to increase the number of Arabs in the force.
Arab commanders who spoke to journalists during the visit said their forces needed more help.
SDF Deputy Commander Qarhaman Hasan said he wanted armoured vehicles, machine guns, rocket launchers and mortars.
The SDF currently had to rely on smuggling to get weapons, he said.
"You can't run an army on smuggling," he added.
Tribal leaders also called on the U.S. to do more, both militarily and with humanitarian aid.
The U.S. has about 200 military advisers in Syria, where 270,000 people have died in five years of civil war.
