An EgyptAir flight disappeared over the Mediterranean Sea en route from Paris to Cairo on Thursday (May 19), triggering a search and rescue operation by the Egyptian and Greek militaries. Officials said they believed the jet has come down in the sea.

Flight MS804, with 66 people on board, disappeared from radars while cruising above the Mediterranean at 2.29am Cairo time (8.29am Singapore time), 45 minutes before it was due to land at 3.15am, EgyptAir said.

In a possible breakthrough, Greek state TV said authorities had found what they said were aircraft parts in the southern Mediterranean, Reuters reported. Earlier, Greek officials said pieces of plastic had been found in the sea some 230 miles (370km) south of the island of Crete. Two life vests which appeared to be from an aircraft were also found.

French president Francois Hollande in a televised press conference confirmed that the plane has crashed. "We must ensure that we know everything on the causes of what happened. No hypothesis is ruled out or favoured," he said. The Paris prosecutor's office said its accident department had opened an investigation into the crash.

Speaking at a news conference, Egypt's minister of civil aviation Sherif Fathy said that a terrorist attack was more likely to have taken down the aircraft than a technical failure.

There were no known security concerns about passengers aboard the missing plane but further checks are underway, Fathy told a news conference, adding that authorities had made failed attempts to contact the plane. But he added that it was still too early to draw any conclusions as to the cause of the plane's disappearance.

Meanwhile, Egypt's foreign ministry exchanged condolences with France on Thursday over what it called the "fall" of the EgyptAir flight - the first official admission that those on board were likely to have died. It said in a statement that Egypt and France had agreed to cooperate closely in investigating the causes of the incident.

PLANE SWERVED IN MID-AIR

Sources told Reuters the objects found appeared to be pieces of plastic in white and red. They were spotted close to an area where a transponder signal was emitted earlier, they said.

Greek Defence Minister Panos Kammenos said the Airbus had first swerved 90 degrees to the left, then spun through 360 degrees to the right. After plunging from 37,000 feet to 15,000, it vanished from Greek radar screens. "At 3.39am the course of the aircraft was south and south-east of Kassos and Karpathos (islands)...immediately after it entered (Cairo airspace) and made swerves and a descent I describe; 90 degrees left and then 360 degrees to the right," he told a news conference.

Earlier, a Greek aviation source told AFP the flight had disappeared from Greek radar at around 0029 GMT. "It crashed around 130 nautical miles off the island of Karpathos," the source said. The official said the last communication with the pilot was three minutes before the plane disappeared, and that there had been no distress call.

CONFUSION OVER WHETHER DISTRESS SIGNAL SENT

There was also confusion over whether the missing plane sent a distress signal after it vanished. EgyptAir said in a statement Thursday that a signal had been received by the army at 4.26am local time (10.26am Singapore time), almost two hours after it disappeared. The army denied receiving any message, Reuters said.

EgyptAir said the plane was flying at 37,000ft (11,280m) and disappeared about 10 minutes after entering Egyptian airspace.

Greek air traffic controllers had spoken to the pilot as the jet flew over the island of Kea, the civil aviation department said. No problems were reported, it said, adding that "the pilot was in good spirits and thanked the controller in Greek."

But just ahead of the handover to Cairo airspace, calls to the plane went unanswered. Shortly after exiting Greek airspace, it dropped off radars, Kostas Litzerakis, the head of Greece's civil aviation department, told Reuters. "During the transfer procedure to Cairo airspace, about seven miles before the aircraft entered the Cairo airspace, Greek controllers tried to contact the pilot but he was not responding," he said.

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' some 130 nautical miles south of the island of Karpathos.

The weather was clear at the time the plane disappeared, according to weather reports. Speed and altitude data from aviation website FlightRadar24.com indicated the plane was cruising at the time it disappeared.

Ehab Mohy el-Deen, the head of Egypt's air navigation authority, told The New York Times: "They did not radio for help or lose altitude. They just vanished."

'NOTHING CAN BE RULED OUT'

Both Egypt and Greece said they had dispatched aircraft and naval vessels to search for the aircraft, while the US Navy said a P-3 Orion long-range aircraft was supporting the search. France said it would send planes and boats to aid in the hunt.

British Foreign Secretary Philip Hammond said Britain had also offered its assistance to Egypt, adding that one of its citizens was on board.

PM Ismail told reporters at Cairo airport: "We cannot exclude anything at this time or confirm anything. All the search operations must be concluded so we can know the cause."

In Paris, Hollande also said the cause remained unknown."Unfortunately the information we have ... confirms to us that the plane came down and is lost," he said.

French Prime Minister Manuel Valls also said "nothing can be ruled out". "We are in close contact with the Egyptian authorities, both civil and military," he told RTL radio. "At this stage, no theory can be ruled out regarding the causes of the disappearance."

The White House said on Thursday United States President Barack Obama received a briefing on the missing EgyptAir plane, its adviser for homeland security and counter-terrorism said.

The aircraft was carrying 56 passengers - with one child and two infants among them - and 10 crew, EgyptAir said. It also gave the nationalities of the passengers: 30 Egyptians, 15 French, two Iraqis, with the rest coming from Britain, Belgium, Sudan, Chad, Portugal, Algeria, Kuwait, Saudi Arabia, and Canada.

Ahmed Abdel, the vice-chairman of EgyptAir's holding company, had told CNN there was no distress call from the plane. Neither was there any "recorded snags" from Paris's Charles de Gaulle airport or from Cairo, he said.

The captain on flight has 6,275 flying hours of experience, including 2,101 on an A320, EgyptAir tweeted. The co-pilot has 2,766 hours of experience, it said.

"NO ONE KNOWS ANYTHING"

At Cairo airport, authorities ushered families of the passengers and crew into a closed-off waiting area, Reuters reported. Two women and a man, who said they were related to a crew member, were seen leaving the VIP hall where families were being kept. Asked for details, the man said: "We don't know anything, they don't know anything. No one knows anything."

Ayman Nassar, the family of one of the passengers, also walked out of the passenger hall with his daughter and wife in a distressed state. "They told us the plane had disappeared, and that they're still searching for it and not to believe any rumours," he said.

A mother of flight attendant rushed out of the hall in tears. She said the last time her daughter called her was Wednesday night. "They haven't told us anything," she said.

SAFETY, SECURITY CONCERNS OVER EGYPT

Several scenarios could explain the flight's mysterious disappearance but experts said a terrorist attack was the most likely. Both France and Egypt have been leading targets for Islamist extremists in recent months.

Experts say the chances of a mechanical malfunction in the case of Thursday's Egyptair disappearance are slim. "A major technical fault - the explosion of a motor, for instance - seems improbable," said aeronautics expert Gerard Feldzer, underlining that the A320 in question was "relatively new", having entered service in 2003.

In addition, the A320 has an excellent safety record as the best-selling, medium-range airliner in the world. An A320 takes off or lands every 30 seconds around the world, Feldzer said.

"It's a modern plane, the incident happened in mid-flight in extremely stable conditions. The quality of the maintenance and the quality of the plane are not in question in this incident," Jean-Paul Troadec, former director of France's aviation Bureau of Investigation and Analysis, told Europe 1 radio.

The head of Russia's FSB security service Alexander Bortnikov said that the possible crash of the EgyptAir jet was"in all likelihood" caused by a terrorist act, the RIA news agency reported, although he gave no evidence of how that had been determined.

The mishap came less than two months after another EgyptAir flight bound for Cairo from Alexandria was hijacked and diverted to Cyprus in a bizarre episode. A 58-year-old Egyptian man commandeered the plane, with 55 passengers on board, using a fake suicide belt. Most of the passengers were quickly released after the plane landed but it took six hours of negotiations, including a conversation with the man's estranged ex-wife, before he surrendered to police.

Concerns have also been raised about security at Egyptian airports after a Russian airliner was downed on Oct 31 last year over the Sinai Peninsula, killing all 224 people on board. The Islamic State in Iraq and Syria (ISIS) group claimed to have smuggled a bomb on board. An EgyptAir mechanic, whose cousin had joined ISIS, was suspected of planting the bomb, Reuters reported in January, citing sources familiar with the matter.

PREVIOUS EGYPTAIR CRASHES

EgyptAir has a fleet of 57 Airbus and Boeing jets, including 15 of the Airbus A320 family of aircraft, Reuters reported.

The missing aircraft was made in 2003. The Paris-Cairo flight was its fifth flight of the day, following trips to Asmara, Eritrea and Carthage in Tunisia, the Guardian said.

Aviation analyst Alex Macheras told the BBC the Airbus A320 is regularly used for short-haul budget flights and has a good safety record.

The last fatal incident involving an EgyptAir aircraft was in May 2002, when a Boeing 737 crashed into a hill while on approach to Tunis-Carthage International Airport, killing 14 people, reported Reuters.

In October 1999, the first officer of a Boeing 767 deliberately crashed the plane into the Atlantic Ocean about 100km south of Nantucket Island, Massachusetts, killing all 217 people on board.

EgyptAir, which is 100 per cent owned by the Egyptian government and employs 850 pilots, has been struggling financially since the 2011 Arab Spring revolution that sparked protests that topple governments in Egypt and other countries in the region and hit tourism to Egypt.

The airline announced in December 2014 that it had accumulated 10.11 billion Egyptian pounds (S$1.57 billion) in losses over the previous three years.

EGYPTAIR HOTLINE NUMBERS

EgyptAir is offering toll-free numbers for passengers' relatives as follows: 080077770000 from any landline in Egypt, and +202 25989320 from any phone from outside Egypt.