'No theory can be ruled out' on disappearance of EgyptAir plane: French PM

France's Prime Minister Manuel Valls said on Thursday "no theory can be ruled out" in the missing EgyptAir flight which disappeared en route to Cairo from Paris.

"No theory can be ruled out on the cause of this disappearance," said Valls, speaking after the plane vanished from radar over the Mediterranean with 66 people on board.

French President Francois Hollande and his Egyptian counterpart Abdel Fattah al-Sisi have "agreed to cooperate closely" to establish the circumstances of the disappearance as soon as possible, Paris said.

The Egyptian military said it had deployed search aircraft and naval vessels to scour the Mediterranean for signs of the missing Airbus A320.

An EgyptAir official said the search was focused on an area of sea north of the Egyptian coast, without providing a precise location

Related read: Live updates: Egypt, Greece send search teams to locate missing EgyptAir flight MS804