No causes can be ruled out in the disappearance of EgyptAir Flight MS804, officials said Thursday amid the search for the missing jet.
The Airbus A320 vanished early Thursday while en route from Paris to Cairo with 66 people on board. French President Francois Hollande later announced that it had crashed.
French Prime Minister Manuel Valls said information was being gathered to establish what may have happened.
"No hypothesis can be ruled out," he told RTL radio.
Egypt's Prime Minister Sherif Ismail echoed those remarks in statements carried on state media, saying he could not "rule out" the possibility of a terror attack, according to The Associated Press.
French and Egyptian officials said they were cooperating.