After U.S.-backed Kurdish forces drove Islamic State militants from the Iraqi city of Sinjar this month, some of the fighters involved began looting houses of Sunni Arabs suspected of ties to the extremist group.

A week later in the oil-rich region of Kirkuk, Kurdish fighters expelled about 60 Sunni Arab families who had remained in the ruins of one village, according to local officials and residents. They said it was one of more than 50 Arab villages razed or partially demolished by Kurds who recaptured them from Islamic...