OCEAN ISLE BEACH, N.C. (AP) — A discarded cigarette or other smoking materials may have caused a beach house fire that killed seven South Carolina college students, authorities said Friday, though a preliminary investigation failed to nail down the blaze's origin.

Mayor Debbie Smith said the probe conducted by the State Bureau of the Investigation and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives confirmed initial reports that the fire started on the back deck and indicated the cause was accidental.

"There has been absolutely no indication that the fire was intentionally set," Smith said.

But because of the extensive damage, she said, it was impossible for investigators to pinpoint the exact source. Investigators specifically ruled out a grill and an outdoor fireplace, known as a chimenea, as sources, Smith said.