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.

Steve Netherland, the special agent in charge of the State Bureau of Investigation's regional office in Jacksonville, said survivors told investigators there were people smoking at the home. But Netherland declined to say what the students were smoking or speculate further on the fire's cause.

Aside from the prospect of smoking materials, Smith said, "there have been no reports of any other sources of ignition within that area."

The five-bedroom home was engulfed in flames Sunday, killing six students from the University of South Carolina and one from Clemson University who had gathered to enjoy one of the season's last weekends of pleasant beach weather. Six students from USC survived, including one who jumped from a window of the burning home into an adjacent canal.

The students killed all died of smoke inhalation and carbon monoxide poisoning, and state medical examiners have concluded there was no evidence of other injuries.

The preliminary report prepared by the SBI and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, said survivors told investigators there were smoke detectors in the home and they activated during the fire.

A final report on the investigation may not be complete for several weeks.

Funerals were held Friday for Lauren Mahon, one of the USC students, and Emily Yelton, the Clemson student. The University of South Carolina planned to hold a memorial service Wednesday.

President Bush said Friday when he arrived in South Carolina for a fundraiser that the seven killed "had so much hope in their lives."

"I hope the families and loved ones can take comfort that in this great state and around the nation there's a lot of people praying for them," Bush said.