Nothing ruled out: French PM

French Prime Minister Manuel Valls. (Getty Images)

France is ruling nothing out as to why an EgyptAir plane went missing after leaving Paris for Cairo, Prime Minister Manuel Valls said on Thursday.

As he spoke on RTL radio, an official at President Francois Hollande's office said the French leader had just spoken to his Egyptian counterpart and that both sides would cooperate closely on the case.

Valls and the official at Hollande's office were speaking as news was emerging that an Egyptian plane that left Paris for Cairo had gone missing with 15 French people among more than 50 passengers aboard according to Egyptian officials.

"We are in close contact with the Egyptian authorities, both civil and military. The Egyptian authorities have already sent air reconnaissance teams to the site, and France is ready to help with the search if the Egyptian authorities ask, of course," Valls told RTL radio.

"At this stage, no theory can be ruled out regarding the causes of the disappearance," Valls said, adding that available information suggested several French citizens were on the flight.