An airliner that was diverted mid-flight because of a bomb threat was being scoured by investigators at Salt Lake City International Airport on Thursday.

Airport spokeswoman Barbara Gann said a flight attendant found a note while the 757 was en route from Denver to San Francisco and turned it over to the pilot.

"The note was threatening enough for the pilot to feel like he should divert," Gann said.

Gann said the passengers and crew were taken to the international terminal, where the FBI planned to interview passengers while trying to figure out the note's origin.

The plane was being searched at a runway away from the airport terminals, where a German shepherd was sniffing luggage on the tarmac.

United Airlines spokeswoman Jean Medina says United Flight 741 requested help from law enforcement authorities and was cooperating with the FBI. She said 168 passengers and six crew were on the flight that departed Denver at 8:23 a.m. MST and was diverted to Salt Lake City at 9:46 a.m. MST.

The North American Aerospace Defense Command says it did not launch fighter jets.