"There were... messages emitted by the plane indicating that there was smoke in the cabin shortly before data transmission broke off," a spokesman of the Bureau of Investigations and Analysis told AFP, adding that it was "far too soon to interpret and understand the cause of the accident as long as we have not found the wreckage or the flight data recorders.
"There were ACAR 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 told AFP.
ACAR, which stands for Aircraft Communications Addressing and Reporting System, 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 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 warnings came about three minutes before air traffic controllers lost contact with the plane at 0029 GMT on Thursday, the Journal said.
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 that the flight control computer malfunctioned, the report said. Wreckage including seats and luggage from EgyptAir Flight 804 were spotted in the eastern Mediterranean as investigators tried to unravel why the plane turned sharply and plunged into the sea.
While Egypt's aviation minister has pointed to terrorism as more likely than technical failure, French Foreign Minister Jean-Marc Ayrault said there was "absolutely no indication" of why the plane went down.
"We're looking at all possibilities," he said, as reports indicated there had been smoke on board and an apparent problem with the flight control system just before it went down.
Families of the 66 people aboard the EgyptAir flight from Paris to Cairo gathered at a hotel near the Egyptian capital's airport after meeting airline officials as they struggled to come to terms with the catastrophe.
"They haven't died yet. No one knows. We're asking for God's mercy," said a woman in her 50s whose daughter had been on board.
French investigators were due to meet their Egyptian counterparts in Cairo, while a French patrol boat carrying equipment capable of tracking the plane's black boxes was expected on Sunday or Monday.
The plane disappeared between the Greek island of Karpathos and the Egyptian coast in the early hours of Thursday, without its crew sending a distress signal.
It had turned sharply twice before plunging 22,000 feet (6,700 metres) and vanishing from radar screens, said Greek Defence Minister Panos Kammenos.
The Wall Street Journal and CNN cited unnamed sources as saying the plane's computer systems sent warning messages indicating smoke in the nose of the aircraft just before air traffic controllers lost contact.
The messages indicated intense smoke in the front portion of the plane. The error warnings also indicated that the flight control computer malfunctioned, the Journal report said.
It said the information was insufficient to determine whether the plane was brought down by a bomb or other causes.
Philip Baum, the editor of Aviation Security International Magazine, told the BBC that technical failure could not be ruled out.
"There was smoke reported in the aircraft lavatory, then smoke in the avionics bay, and over a period of three minutes the aircraft's systems shut down," he said.
"That's starting to indicate that it probably wasn't a hijack, it probably wasn't a struggle in the cockpit, it's more likely a fire on board. Now whether that was a technical fire, a short circuit, or whether it was because a bomb went off on board, we don't know."
Greek civil aviation chief Constantinos Litzerakos said the pilot had mentioned no problem in his last communication.
"The flight controllers contacted the pilot at a height of 37,000 feet... he did not mention a problem," he said.
Personal belongings and parts of the Airbus A320 were spotted by search teams scouring seas off Egypt's northern coast about 290 kilometres (180 miles) from the city of Alexandria, the military said.
Kammenos said the teams, which include multinational aircraft and ships, had found "a body part, two seats and one or more items of luggage".
The passengers included 30 Egyptians, 15 French citizens, two Iraqis, two Canadians, and citizens from Algeria, Belgium, Britain, Chad, Portugal, Saudi Arabia and Sudan. They included a boy and two babies.
Seven crew members and three security personnel were also on board.
The discovery of the wreckage came after the European Space Agency said one of its satellites had on Thursday spotted an oil slick about 40 kilometres southeast of the plane's last known location.
In October, foreign governments issued travel warnings for Egypt and demanded a review of security at its airports after the Islamic State (Isis) group said it downed the Russian airliner over Sinai with a bomb concealed in a soda can that had been smuggled into the hold.
Isis has been waging a deadly insurgency against Egyptian security forces and has claimed attacks in both France and Egypt.