In this March 28, 2018 photo, a Kurdish policeman checks an Arab Syrian man at a checkpoint controlled by The U.S.-backed Syrian Democratic Forces, SDF, on a highway in Hassakeh province, Syria. SDF defeated IS in March but the Kurdish-led force is now facing protests by local Arab tribesmen in Deir el-Zour province. If the protests turn to an all-out uprising against the SDF it could be a blow to Washington as President Trump has plans to reduce America's military presence in Syria. (AP Photo/Hussein Malla)
In this March 28, 2018 photo, a Kurdish policeman checks an Arab Syrian man at a checkpoint controlled by The US-backed Syrian Democratic Forces, SDF, on a highway in Hassakah province, Syria. AP

US-backed forces crack down on ISIS fighters in Syria's Deir Ezzor