(Portland, OR)  --  Police are investigating a report of a sexual assault in North Portland.  Authorities say an 18-year-old woman told officers she was attacked late Wednesday night or early yesterday morning in the area of North Knott Street and Mississippi Avenue.  Police say two suspects are being sought, one black male and one white, both about six feet tall.  Anyone with information helpful to the investigation is asked to call 503-823-1097.