The report said McCain is the highest-ranking U.S. official to enter Syria since the civil war began more than two years ago. McCain, R-Ariz., is a critic of the Obama administration's non-involvement policy in Syria.
The senator made the unannounced visit across the Turkey-Syria border with Gen. Salem Idris, leader of the Supreme Military Council of the Free Syrian Army, The Daily Beast reported.
The visit lasted several hours.
While meeting with McCain, rebel leaders urged the United States to provide them with heavy weapons and a no-fly zone, and launch airstrikes on the Syrian regime forces and the forces of Hezbollah, the report said.