By Isabel Coles NEAR SINJAR TOWN (Reuters) - Kurdish forces backed by U.S. air strikes seized the northern Iraqi town of Sinjar from Islamic State on Friday, a Reuters witness said, in one of the most significant counter-attacks since the militants swept through the north last year. "ISIL defeated and on the run," the Kurdistan regional security council said in a tweet, using an acronym for Islamic State. It said Kurdish peshmerga forces, which led the operation, had secured Sinjar's wheat silo, cement factory, hospital and several other public buildings.