On 1 June, a senior U.S. defense official told Fox News that a "thousands"-strong SDF force consisting of Sunni Arab fighter and a small contingent of Kurdish fighters (mainly from the YPG) with assistance by U.S. special forces operators and fighter jets launched an operation to recapture the strategically important ISIL-held city of Manbij in northern Syria, from the border with Turkey; ISIL used the town to move supplies and foreign fighters into Syria from Turkey.