Islamic State resistance “melted” away in the strategically important Syrian city of Shaddadi, giving a rag-tag force of Syrian rebels — backed by U.S. air power and special operations troops on the ground — a key victory after only a few days of combat.

“We expected a tougher fight inside the city,” said Army Col. Christopher Garver, a U.S. Defense Department spokesman in Baghdad.

“All told the [Syrian Democratic Forces] overwhelmed the [Islamic State] force around Shaddadi and isolated the city in just six days, which was much faster than the SDF had estimated for the operation,” Garver said.

The seizure of Shaddadi was the biggest victory to date for the SDF, a coalition of Syrian rebel groups stitched together and armed by the U.S. military. Defense Secretary Ash Carter pointed to the operation as validation of the Pentagon’s current strategy.

“This is just the most recent example of how we’re effectively enabling and partnering with local forces to help deal ISIL a lasting defeat,” Carter said during testimony on Capitol Hill. Seizing the town will “sever the last major northern artery between Raqqa and Mosul,” he said.

The Syrian forces were backed by dozens of U.S. special operations troops who have been in Syria for several months to help coordinate the array of local militias fighting the Islamic State, also known as ISIS or ISIL.

Those special forces were in the Shaddadi area to advise and assist the SDF combat units, but the Americans remained several miles away from the front-line fighting, Garver said.

“They are not down on the fight” Garver said. “They are on a more stationary headquarters where they can help plan command-and-control.”