Investigators are looking into whether a device was placed on the aircraft in Tunis or Asmara before it landed in Paris.
The EgyptAir flight MS804 that crashed in the Mediterranean could have been downed by a smuggled Lockerbie-style timed bomb, it's feared.
Investigators are looking into whether a device was placed on the Airbus A320 from Paris to Cairo before it went missing with 66 people on board, including one Brit, in the early hours of this morning.
Wreckage from the plane , which had been flying 10 miles inside Egyptian airspace when it made "sudden swerves", has since been discovered near the Greek island of Karpathos.
The plane, which had previously stopped in Eritrea and Tunisia, plunged 22,000ft while spinning at 360 degrees before disappearing off radar.
A British dad-of-two, Richard Osman, is feared to be among those travelling on the plane when it crashed.
Investigators are looking into whether a Lockerbie-style device was placed on the aircraft in Tunis or Asmara before it landed in Paris.
It was on its fifth journey of the day, having already flown from Paris to Cairo and back, and been to Tunisia and Eritrea.
Sources said it spent just 90 minutes on the tarmac before setting off from Charles de Gaulle for Cairo.
Ground crews and screening staff who were working at Charles de Gaulle and Tunis airports are to be quizzed.
And French sources said CCTV footage from inside Terminal 1 and airside at the airport has already been seized.
More than 86,000 French airport workers were checked after the Paris terror attacks last year.
Around 60 staff in the French capital had their authorisation revoked in December due to their links with Islamic extremism.
In the UK, almost 100,000 people work at the two big London airports alone – 78,500 at Heathrow, and 21,000 at Gatwick.
Phil Giles, a former investigator with the UK’s Air Accidents Investigation Branch, said a 'Lockerbie-style' device was a possible culprit.
He said: “It’s a real mystery, but it sounds at this early stage that there could have been a device, placed on the plane earlier at another airport in some kind of Lockerbie situation.
“It may have been placed on board at Paris, though security is very tight there already. We may see a focus on the air-side staff there in the coming days.”
Aviation experts also say the unexplained sharp turns before the tragedy raise fears there could have been a struggle inside the cockpit.
Panos Kammenos, the Greek defence minister, said the aircraft made a series of sharp turns at 2.30am local time.
He said: “It turned 90 degrees left and then a 360-degree turn toward the right.
“It dropped from 38,000 to 15,000 feet and then it was lost at about 10,000
feet.”
Paul Charles, an aviation analyst, believes the sudden swerves indicate an incident on the flight deck.
He said: “It does suggest it wasn’t necessarily blown out of the sky by a missile.
“It wasn’t necessarily a device on board. It would suggest the pilot has been involved in some some in an incident in the cockpit.”
The tragedy happened seven months after 224 people were killed when a Russian aircraft crashed over Egypt’s Sinai Peninsula.
Russia, US and British authorities believe a bomb on board the jet was the most likely cause of the tragedy.
Islamic State claimed responsibility at the time saying it had downed the jet with a bomb but Egypt rejected the claims.
The terror group, behind the Paris massacres last year, issued a fresh threat to France days ago.
56 passengers, seven crew members and three airline security personnel died when Flight MS804 came down near the Greek island of Karpathos.
A child and two babies were among the passengers, including 30 Egyptians,
15 French nationals and two Iraqis, who died.
There were also travellers from Belgium, Kuwait, Saudi Arabia, Sudan, Chad,
Algeria, Portugal and Canada.
The Egyptian co-pilot was named by friends on social media as Mohamed Mamdouh Assem, from Cairo.
A Greek defence ministry source said the captain of a merchant ship saw a "flame in the sky" in the area at the time of the crash.
There were unconfirmed reports of search teams discovering debris and life-jackets believed to be from the plane in the sea south of Crete.
A Royal Navy warship and RAF search plane are due to join the recovery operation today.
Egyptian authorities said the aircraft was more likely to have been brought down as a result of a terrorism than technical failure.
Alexander Bortnikov, head of Russia’s FSB spy agency, said the tragedy was “in all likelihood” caused by a terrorist act.
And aviation expert Jean-Paul Troadec said all the indications pointed towards the “brutal event” being a terror attack.
He said: “There’s a strong possibility of an explosion on board from a bomb or a suicide bomber.”
Mr Troadec, former head of the French air accident investigation bureau,
said a technical accident was “not that likely”.
Egypt’s prosecutor general ordered a state security investigation into the disappearance, which occurred in good weather conditions.
Just two months ago a domestic EgyptAir flight was hijacked and forced to make an emergency diversion to Cyprus.
French president Francois Hollande confirmed the aircraft, which departed Paris at 11.09pm local time, had come down.
He told reporters: “I have been informed that the aircraft that left Paris to go to Cairo has been lost. It crashed.”
Mr Hollande, who said “no hypothesis is excluded”, spoke via phone with his Egyptian counterpart Abdel-Fatah el-Sissi.
The pilot of Flight MS804 had logged 6,275 flying hours, including 2,101
hours on the A320.
Greek air traffic controllers spoke to him as the jet flew over the island of Kea.
But when they tried to contact the plane before it left the country’s airspace, the calls went unanswered.
Kostas Litzerakis, head of the country’s civil aviation department, said disappeared from radar screens soon afterwards.
An unnamed Cairo airport official told local media that the pilot did not send a distress signal.
He said the last contact was 10 minutes before it vanished, prior to it entering Egyptian airspace.
Ahmed Adel, vice chairman of EgyptAir's parent company, said there was no special cargo or dangerous goods on the flight.
He said: “It just lost contact and we lost it on the radar of the air traffic controllers.”
Ehab Mohy el-Deen, head of the Egyptian air navigation authority said: “They did not radio for help or lose altitude. They just vanished.”
Air travel expert Julian Bray said no alert being made could mean the airliner suffered a "catastrophic failure”.
He said: “Everything went dead and they wouldn't have had time to get a message out. It's gone into the deepest part of the Mediterranean.”
