Aircraft was carrying 56 passengers, including one child and two infants, and 10 crew, EgyptAir said. They included 30 Egyptian and 15 French nationals, along with nationals from 10 other countries.
"The theory that the plane crashed and fell is now confirmed after the preliminary search and after it did not arrive at any of the nearby airports," said a senior aviation source, who declined to be identified.
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"There was nothing unusual," EgyptAir vice chairman Ahmed Adel told Reuters. "The search and rescue aircraft from the Egyptian air force are at the position where we lost contact. They are still looking and so far there is nothing found."
Egyptian state newspaper Ahram reported no distress call was made and the last contact was 10 minutes before the plane disappeared.
The pilot had clocked up 6,275 hours of flying experience, including 2,101 hours on the A320, while the first officer had 2,766 hours, the airline said.
Greek air traffic controllers spoke to the pilot as the jet flew over the island of Kea, in what was thought to be the last broadcast from the aircraft.
"The pilot did not mention any problems," Kostas Litzerakis, the head of Greece's civil aviation department, told Reuters.
However, during the transfer to Cairo airspace, Greek controllers were unable to reach the pilot and the plane vanished from their radars shortly after leaving Greek airspace, he added.
Greece said it had deployed aircraft and a frigate to the area to help with the search.
A Greek defence ministry source said authorities were also investigating an account from the captain of a merchant ship who reported a 'flame in the sky' about 130 nautical miles south of the island of Karpathos.
The weather was clear at the time the plane disappeared, according to Eurocontrol, the European air traffic network. "Our daily weather assessment does not indicate any issues in that area at that time," it said.
Speed and altitude data from aviation website FlightRadar24.com indicated the plane was cruising at the time it disappeared.
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