Southwest flight 2675 departed Los Angeles at 2:12 p.m. local time Monday, but an unspecific threat forced the landing of the aircraft in Phoenix at 3:57 p.m. local time, The Arizona Republic of Phoenix reported.
Two F-16s monitored the flight as it landed and was moved to an isolated area of the Phoenix Sky Harbor International Airport, a NORAD spokesman, whose name was not reported, said.
The FBI and Phoenix police bomb squad and K9 units boarded the plane and conducted an extensive search, the newspaper reported. They examined each piece of luggage and questioned all 143 people on board the aircraft late into the evening Monday.
"We want to use an abundance of caution," said Phoenix police Sgt. Steve Martos.
The investigation restricted runway access for the western portion of the airport, delaying flights and disrupting traffic outside the facility, the Republic reported.
A second plane was made available to take the 143 passengers to their intended destination in Austin, the newspaper said.