Passengers on a Southwest Airlines flight heading from Los Angeles, Calif. to Austin, Texas experienced a bit of a diversion on Monday. A bomb threat was called in about the plane, leading to that flight being grounded in Phoenix, Ariz.

Southwest Airlines flight 2675 landed safely in Phoenix at about 3:30 p.m. local time. Though nobody was hurt during the incident, there was plenty of concern for all 143 passengers aboard the aircraft.

F-16 fighter jets were diverted from Davis-Monthan Air Force Base in Tucson, Ariz. to "monitor the situation from the air," said Michael Kucharek, a spokesperson for the North American Aerospace Defense Command. "It was serious enough that we diverted aircraft from their original flight plan."

Once the plane was grounded, the passengers and crew were escorted off the aircraft and authorities were sent in to search for any evidence of a bomb aboard. They did not find anything suspicious during their search. Despite the surprise landing, the bomb threat did not do much to derail the Phoenix airport's schedule.

"The plane has been isolated and is not parked near the terminal areas. Flights at Sky Harbor are arriving and departing as scheduled," Phoenix Sky Harbor International Airport spokesperson Julie Rodriguez said.

It is still uncertain what the motive for the bomb threat may have been. The investigation continued Tuesday, though no arrests or substantial leads have yet been made. Passengers have been assured they will be transported to Austin "as soon as possible," but officials are making sure they get as much information as they can first.

"All passengers were interviewed by Monday evening, FBI special agent Manuel Johnson said in a statement. Investigators were making all efforts to identify the caller who made the bomb threat," noted an ABC News.

That bomb threat Monday was followed by three other, and supposedly all unrelated, incidents Tuesday. There were bomb threats at Princeton University, Virginia's Richmond airport, and governmental buildings near Georgia's state capitol in Atlanta.