French President Francois Hollande confirmed that the EgyptAir flight that disappeared Thursday en route to Cairo from Paris with 66 passengers and crew on board has crashed.
"We must ensure that we know everything on the causes of what happened. No hypothesis is ruled out or favored," he said in a televised address.
The plane made sudden turns and a sharp descent before disappearing from the radar, Greek Defense Minister Panos Kamennos told a news conference.
'It turned 90 degrees left and then a 360- degree turn toward the right, dropping from 38,000 (11,582 meters) to 15,000 feet (4,572 meters) and then it was lost at about 10,000 feet (3,048 meters),'' he said.
Greek and Egyptian crews are searching for the missing aircraft.
Greek officials said the search was taking place at sea, about 130 nautical miles southeast of the island of Karpathos.
French Foreign Minister Jean-Marc Ayrault said France will contribute planes and boats to the search, and that they are maintaining close contact with Egyptian authorities. "We are at the disposal of the families – that is the priority ... which is why we are in constant contact with the Egyptian authorities," he said at a news conference near Paris.
The French and Egyptian foreign ministers exchanged condolences over the incident.
Too early to tell
Egyptian Prime Minister Sherif Ismail told reporters gathered at Cairo's airport it was too early to say whether a technical problem or a terror attack caused the plane to crash. "We cannot confirm or deny anything at this point, until the investigation is underway, and based on it, we can say what the situation is," he said.
The carrier said that it lost contact with Flight MS804 at 2:30 a.m. Cairo time, when the Airbus A320 was at an altitude of about 11,278 meters and approximately 16 kilometers inside Egyptian airspace.
The airline said earlier Egyptian armed forces received a distress message before communication with the plane was lost; however, a military spokesman later posted on his Facebook page a statement denying a distress call had been received.
Fifty-six passengers were on board, including one child and two infants. Saudi officials say the flight included passengers from France, Britain, Egypt, Iraq, Kuwait, Saudi Arabia, Sudan, Chad, Portugal, Algeria and Canada. No U.S. citizens were reported among the missing.
IN PICTURES: Waiting for news at Cairo Airport
See previous crashes and hijackings involving EgyptAir
EgyptAir has released phone numbers specifically for the families of passengers, and provided translators and doctors in the Cairo airport.
Aviation experts are currently warning against speculation, reiterating that at this point too little is known to draw any conclusions.
“I will say that when an airplane disappears at 37,000 feet, it’s a highly unusual event," Scott Hamilton of Leeham Aviation Consultancy told VOA. "It either typically indicates a catastrophic failure, catastrophic emergency of some kind, or as we know from not too long ago a bomb could go off ... but you just have to be cautious and not jump to any conclusions at this point."
Hamilton explained that a search team would most likely go to the last point where the plane could be traced and search for debris. Upon finding debris, either a search and rescue or search and recovery team would be dispatched to locate survivors and bodies.
"They would be ultimately looking for the airplane's main records and black boxes," he added.
FILE - An Egyptair Airbus A320 airbus stands on the runway at Larnaca Airport in Larnaca, Cyprus.
The disappearance has renewed security concerns months after a Russian passenger plane blew up over the Sinai Peninsula. The Russian plane crashed in Sinai on October 31, killing all 224 people on board. Moscow said it was brought down by an explosive device, and a local branch of the extremist Islamic State group claimed responsibility for planting it.
In 1999, EgyptAir Flight 1990 crashed into the Atlantic Ocean near the island of Nantucket, off the coast of the U.S. state of Massachusetts, killing all 217 people aboard. U.S. investigators filed a final report that concluded its co-pilot switched off the autopilot and pointed the Boeing 767 downward. But Egyptian officials rejected the notion of suicide altogether, insisting some mechanical reason caused the crash.
A relative of the victims of the EgyptAir flight 804 that crashed, reacts as she makes a phone call at Charles de Gaulle Airport outside of Paris, Thursday, May 19, 2016.
Additional reporting by VOA's Victor Beattie in Washington, D.C. VOA's Steve Herman contributed to this report, as well as Lisa Bryant from Paris.