Two Air France flights headed from the United States to Paris were diverted Tuesday night due to bomb threats, officials said.
Both flights landed safely.
Flight 65, headed from Los Angeles to Paris, was diverted to Salt Lake City after a bomb threat was called in from the ground, a U.S. government official said.
The official did not know if anyone was arrested and was not aware of any unruly passengers on board.
Shortly afterward, Air France Flight 55 from Washington's Dulles International Airport to Charles de Gaulle Airport in Paris was diverted to an airport in Halifax, Nova Scotia -- also due to a bomb threat, a government source said.
The source did not know if the same person called in both threats.
"Several law enforcement agencies are working to determine the nature of the threats which caused the aircraft to divert," FBI Special Agent Todd Palmer of the Salt Lake City division said.
No U.S. military aircraft were scrambled in either of the reported Air France incidents, NORAD spokesman Preston Schlachter said.
"Diversion of flights are the most draconian response to a bomb threat," CNN national security analyst Juliette Kayyem said. "I think right now we take this seriously until we hear some explanation to the validity of the bomb threat."
Passengers questioned by FBI
Passenger Trevor Moran was headed to Paris from Los Angeles to shoot a music video on Flight 65.
He said the pilot came on and said the plane had to make an emergency landing.
"There were huge buses when we landed that they loaded us all on," he told CNN.
"Everyone on the flight is waiting in this lobby. Nobody knows what's going on."
Keith Rosso, who was on the same flight, said he had just finished dinner when the flight staff abruptly took trays away and said the plane was landing due to 'unsafe flying conditions."
Rosso said the FBI was interviewing passengers on Flight 65.
As for Flight 55, the Royal Canadian Mounted Police said the plane and luggage will be searched for explosives, the agency tweeted.
'This is terrorism'
Even though the flights landed safely, CNN law enforcement analyst Jonathan Gilliam said there are reasons for serious concern.
"One thing that has to be clear is that we may call this a hoax, but the reality is, terrorism -- which we see going on in France right now, and here -- is a tactic used to affect a psychological or political change on a community, and that is what this is," Gilliam said.
"It may be a hoax, as far as a bomb threat. But this is terrorism."
The bomb threats on Paris-bound flights came four days after a wave of deadly attacks terrorized the French capital.
At least 129 people were killed in an onslaught of bombings and shootings Friday night. French President Francois Hollande declared a state of emergency.
The terror group ISIS claimed responsibility. Afterward, French warplanes have launched waves of airstrikes on ISIS' de facto capital of Raqqa, in northern Syria.