The EgyptAir A320 that crashed into the Mediterranean with 66 people aboard had transmitted automatic messages indicating smoke in the cabin, the French aviation safety agency said.
"There were ACAR [Aircraft Communications Addressing and Reporting System] messages emitted by the plane, indicating that there was smoke in the cabin, shortly before data transmission broke off," a spokesman of France's Bureau of Investigations and Analysis said.
ACAR is a digital system that transmits short messages between aircraft and ground stations.
The spokesman said it was "far too soon to interpret and understand the cause of Thursday's accident, as long as we have not found the wreckage or the flight data recorders".
The signals indicated there was smoke in the front toilets near the cockpit, an expert told AFP.
According to the specialised aviation website Avherald, the ACAR messages read "smoke lavatory smoke" then "avionics smoke" — referring to the plane's electronic systems — then a "fault" with the FCU, the pilots' flight control unit in the cockpit.
The warnings began about three minutes before air traffic controllers lost contact with the plane.
The Wall Street Journal, citing people familiar with the matter, earlier reported that automated warning messages indicated smoke in the nose of the aircraft and an apparent problem with the flight control system.
The messages indicated intense smoke in the front portion of the plane, specifically the lavatory and the equipment compartment beneath the cockpit.
The error warnings also indicated the flight control computer malfunctioned, the report said.
CNN also reported smoke alerts on the flight minutes before it crashed, citing an Egyptian source.
The editor of Aviation Security International Magazine, Philip Baum, said the smoke indicated the plane was probably not hijacked.
But he said it was still possible there was a bomb on board or the smoke was caused by a technical fire.
On Friday, search teams found wreckage including seats and luggage about 290 kilometres north of Egypt's coastal city of Alexandria, Egypt's military said.
The plane disappeared without any distress signal between the Greek island of Karpathos and the Egyptian coast.
It had turned sharply twice in Egyptian airspace before plunging 6,700 meters and vanishing from radar screens, Greek Defence Minister Panos Kammenos said.
AFP