CAIRO — Egypt and Greece mounted a marine search-and-rescue operation in the southern Aegean Sea early Thursday for an EgyptAir passenger jet with 66 people on board that suddenly disappeared over the Mediterranean shortly before it was due to land in Cairo.
The reason for the plane’s disappearance was unclear, but the developments touched off fears about terrorism and investigations in Egypt, Greece and France, where the plane took off. Aviation security in Egypt has been under intense scrutiny since a bomb brought down a Russian airliner over the Sinai Peninsula in October, killing all 224 people on board, and France has tightened airport security after a series of terrorist attacks last year.
However, the Egyptian authorities were adamant that their investigation was only in its beginning stages. EgyptAir chided news outlets for spreading “misleading information” and said on Twitter that “the reason of disappearance hasn’t been yet confirmed.”
EgyptAir Flight 804 departed Paris at 11:09 p.m. on Wednesday and disappeared at 2:45 a.m., shortly after it entered Egyptian airspace, EgyptAir said on Twitter. The plane had been traveling at an altitude of37,000 feet and was carrying 56 passengers, including three children; seven crew members; and three members of airline security personnel.
EgyptAir said it had last made radar contact with the plane at 2:30 a.m., when it was 175 miles off the Egyptian coast. The plane’s pilot had spoken to Greek air traffic controllers four minutes earlier, and had not indicated that there was any problem, according to a spokesman for the Hellenic Civil Aviation Authority. “Within three minutes, communication was lost,” he said.
At 3:14 a.m. Cairo time, the Greek authorities began a search operation, deploying a C-130 military transport plane. At 4:26 a.m. — nearly two hours after the last radar contact — the plane emitted a signal, although it was not clear whether that was an emergency distress signal sent by a crew member or an automated signal from the plane’s onboard computers.
“We don’t know if the pilot had something to do with this or if it is just the plane sending it,” said Ihab Raslan, a spokesman for the Egyptian Civil Aviation Ministry.
Greece said it had sent two planes, including the C-130, along with the naval frigate Nikiforos Fokas and two Super Puma rescue helicopters to an area around the island of Karpathos in the southern Aegean Sea.
The Egyptian military said that it had deployed aircraft and naval vessels to search for the plane in cooperation with Greece. “We are looking everywhere on land and at sea,” said Mohamed Samir, a military spokesman.
A list of the 56 passengers’ nationalities released by EgyptAir said that 30 were from Egypt, 15 from France, two from Iraq and one each from Algeria, Belgium, Britain, Canada, Chad, Kuwait, Portugal, Saudi Arabia and Sudan.
At the airport in Cairo, relatives and friends waiting for the passengers were shepherded into a separate area, many of them red-faced and crying. Aviation security officials banned journalists from filming and interviewing people, saying they were acting on orders from the Interior Ministry, which controls the police.
In a flurry of posts on Twitter on Thursday, EgyptAir emphasized the experience of the crew of the missing airliner, an Airbus A320. The pilot has more than 6,000 flying hours, and the co-pilot has 2,700 hours, the airline said.
The office of President François Hollande of France said in a statement Thursday morning that he had spoken over the phone with the Egyptian president, Abdel Fattah el-Sisi, about the flight, and that the two countries would cooperate.
Speaking on the French radio station RTL, Prime Minister Manuel Valls said that the French authorities were still gathering information about the disappearance and that, “at this stage, no hypotheses on the causes of this disappearance can be ruled out.”
In the October crash of the Russian jetliner, the plane broke up in midair 23 minutes after takeoff from the Red Sea resort city of Sharm el Sheikh. The Islamic State, whose local affiliate is fighting the Egyptian military in the Sinai Peninsula, claimed that it had brought down the plane, an Airbus A321-200.
Egypt initially denied that the crash was connected to terrorism, even as Russia and Britain said that they that believed a bomb was responsible. But in February, Mr. Sisi said that the flight had been brought down by terrorists, although he did not specify by which group.
The crash dealt a crippling blow to Egypt’s beleaguered tourism industry, which had already declined sharply in recent years. It also helped precipitate a decline in the value of the Egyptian currency in recent months.
Russia and Britain have suspended flights to Sharm el Sheikh since the crash. The Egyptian investigation has yet to officially identify the exact cause. But President Vladimir V. Putin of Russia and Mr. Sisi discussed the resumption of flights in a telephone call on May 10, according to a statement from the Kremlin.
The last major crash involving an EgyptAir plane occurred in 2002 when a Boeing 737 traveling to Tunis from Cairo crashed into a hill near the Tunis airport, killing 18 of the 62 people on board.
In March, a hijacker wearing a fake explosives vest diverted an EgyptAir domestic flight to the island of Cyprus, where an hourslong standoff result in his arrest and no injuries to passengers. The Cypriot authorities later described the man, Seif Eldin Mustafa, who said he wanted to free female prisoners from Egyptian jails, as “psychologically disturbed.” He is currently battling extradition to Egypt.
Security at Charles de Gaulle Airport outside Paris was tightened after the terrorist attacks in and around the French capital in November, and scrutiny of passengers and luggage was also stepped up in the wake of the bombing of Brussels Airport in March.
After the November attacks, French authorities have used the threat of terrorism to justify raids of employee lockers at Charles de Gaulle, as well as a systematic review of the roughly 87,000 airport employees who have badges giving them access to secure areas that include the tarmac, baggage handling and cargo storage. Those reviews have led the authorities to revoke dozens of badges for security reasons, according to the airport police.
Rules that ban passengers from carrying liquids, gels and aerosols in hand luggage were also extended to apply to airline and airport personnel as well as anyone with access to secure areas of the airport.
Egypt has come under criticism in the past for its lack of transparency in aviation accidents. In 1999, an EgyptAir flight crashed into the Atlantic Ocean shortly after takeoff from John F. Kennedy Airport in New York, killing all 217 people on board.
Although American investigators concluded that the co-pilot had steered the airplane in the sea, Egypt rejected the idea of suicide and still insists that the crash was caused by an unspecified mechanical failure.