France's air accident investigation agency, Le Bureau d'Enquêtes et d'Analyses (BEA), has confirmed that EgyptAir sent signals that smoke was detected before the plane crashed in the Mediterranean.
However a BEA spokeperson said the signals did not explain what caused reported smoke on Flight MS804 which was en route from Paris to Cairo with 66 passengers and crew when it vanished early on Thursday (local time).
The spokesperson said the priority was now to find the missing flight recorders of the EgyptAir jet.
Smoke was detected in the toilet and the aircraft's electrics just minutes before the signal was lost, according to initial reports from data published on the air industry website The Aviation Herald.
Search teams looking for the plane have discovered human remains, seats and passengers' belongings in the Mediterranean Sea.
The debris was discovered about 290km north of Alexandria, just south of where the signal from the plane was lost on Thursday, local time, the Egyptian military said.
European Space Agency satellites spotted an oil slick in the area where the flight had vanished but the organisation said there was no guarantee it was from the missing plane.
Egyptian President Abdel Fattah al-Sisi has expressed his "utmost sadness and regret" at the crash.
Initial reports late on Thursday, based on Egyptian officials' comments that wreckage had been found, later proved unfounded and were dismissed by Greek officials.
Greece has not yet commented on the latest discovery.
Greek, Egyptian, French and UK military units have been taking part in a search operation near Greece's Karpathos island.
Greece said radar showed the Airbus A320 had made two sharp turns and dropped more than 25,000ft before plunging into the sea.
Egypt said the plane was more likely to have been brought down by a terrorist act than a technical fault.
However, there has been "absolutely no indication" so far as to why the plane came down, French Foreign Minister Jean-Marc Ayrault said on Friday morning.
Three investigators from the French air accident investigation bureau, along with a technical adviser from Airbus, have joined the Egyptian inquiry.
Most of the people on board Flight MS804 were from Egypt and France. A Briton was also among the passengers.
The BBC has learned the plane that disappeared was forced to make an emergency landing in 2013 after the pilot noticed the engine overheating, but an official report said the defect had been repaired.
In France, the focus is on whether a possible breach of security happened at Paris Charles de Gaulle airport.
After last November's Paris attacks, some airport staff had their security clearance revoked over fears of links to Islamic extremists.
Eric Moutet, a lawyer for some of those employees, told the BBC that there had been attempts by Islamists to recruit airport staff.
"That is clear.
"There are people who are being radicalised in some of the trade unions, etc. The authorities have their work cut out with this problem," he said.
In October, an Airbus A321 operated by Russia's Metrojet blew up over Egypt's Sinai Peninsula, with all 224 people on board killed.
Sinai Province, a local affiliate of the Islamic State jihadist group, said it had smuggled a bomb on board.
Flight MS804 left Paris at 11.09pm (local time) on Wednesday and was scheduled to arrive in the Egyptian capital soon after 3.15am on Thursday.
On the plane were 56 passengers, seven crew members and three security personnel.
Greek aviation officials said air traffic controllers spoke to the pilot when he entered Greek airspace and everything appeared normal.
They tried to contact him again at 2.27am (Cairo time), as the plane was set to enter Egyptian airspace, but "despite repeated calls, the aircraft did not respond".
Two minutes later it vanished from radar.
- BBC / Reuters