America’s top military officer said Friday up to 15,000 moderate Syrian rebels would be needed to dislodge Islamic State militants from their strongholds in northern and eastern Syria.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, made the assessment to reporters a week after Congress approved a plan to begin training and equipping 5,000 moderate Syrian rebels to take on the Islamic State, which has seized about a third of the territory in Syria and neighboring Iraq.

“Five thousand has never been the end state,” Dempsey said. “Twelve to 15,000 is what we believe they would need to recapture lost territory in eastern Syria” that the Islamic State controls. […]