– Nearly a year into a bombing campaign intended to degrade and destroy the Islamic State in Iraq and the Levant, the U.S. finally may have found a reliable partner on the ground in Syria.

In comments Monday, Defense Secretary Ashton Carter acknowledged that Kurdish fighters from the YPG militia are identifying bomb targets for U.S.-led airstrikes. He referred to the militia as "capable," praised its "effective action," and said that because of the Kurds' actions, U.S. forces had been able to "support them tactically."

It was the first public description by a senior Obama administration official detailing the cooperation between the U.S. and the militia, to which NATO ally Turkey has objected.

The militia's success is one of the reasons the U.S. is intensifying its bombing campaign against ISIL in Syria, Carter said.

"That's what we were doing over the weekend north of Raqqa, which is conducting airstrikes that limit ISIL's freedom of movement and ability to counter those capable Kurdish forces," Carter said.

Carter's singling out of the YPG, or the People's Protection Units, comes after months in which U.S. officials have said they were putting off a more concerted campaign in Syria in favor of pressing against ISIL in Iraq because the U.S. lacked a capable ground partner in Syria.

But Carter praised the YPG's recent successes against ISIL. Backed by U.S. air power, he said, YPG forces have advanced to within 18 miles of Raqqa, ISIL's main stronghold in Syria.

"That's the manner in which effective and lasting defeat of ISIL will occur, when there are effective local forces on the ground," Carter said.