The French aviation safety agency said that the EgyptAir A320 that crashed into the Mediterranean with 66 people aboard had transmitted automatic messages indicating smoke in the cabin.

"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 news agency on Saturday.

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."

Flight data, as published on The Aviation Herald website, suggested that smoke alarms were set off on EgyptAir Flight 804 minutes before it crashed.

The Aviation Herald website, which tracks the aviation industry, said it received information that smoke alarms went off in the toilets of the Airbus A320 before the crash.

The signals were reportedly sent from three independent sources which passed on data from the ACARS.

"So many signals coming out at the same time are indicative of a fire on board the plane," David Gleave, a senior independent aviation safety investigator, told Al Jazeera. "We need to know what started it. We need to recover the air frame to determine that."

The Egyptair Airbus 320, from Paris to Cairo, vanished early on Thursday shortly after leaving Greek airspace.

The plane had been cruising normally in clear skies on the nighttime flight to Egypt's capital when it suddenly lurched left, then right, spun all the way around and plummeted 38,000 feet into the sea, never issuing a distress signal.

Egyptian authorities have said they would investigate reports of smoke alerts.

"We are looking into this report," an Egyptian civil aviation ministry official told the AFP news agency. "At this point I can't deny or confirm it."

Human remains found

Human remains, luggage and airline debris were retrieved Friday from the sea, around 290km north of the Egyptian coastal city of Alexandria.

The European Space Agency said a satellite on Thursday spotted a possible 2km-long oil slick, about 40km south-east of the last-known location of the plane.

The two black boxes from Egyptair Flight MS804 have yet to be discovered, and the cause of the crash is unknown.

Experts said answers will come only with an examination of the wreckage, the plane's cockpit voice and the black boxes.

The search for wreckage was to intensify on Saturday, as French Foreign Minister Jean-Marc Ayrault was to meet relatives of the 15 French victims in Paris.

EGYPTAIR CRASH: More wreckage found north of Alexandria

Richard Marquise, a former FBI agent who led the US task force investigating the Lockerbie bombing, told Al Jazeera that Egypt was quick to point to an attack, unlike France.

"It's becoming a game of finger-pointing about who's responsible, whether it's a mechanical failure of EgyptAir, or a terrorist bomb on the aircraft," he told Al Jazeera.

He added that this was in contrast to the October 2015 Metrojet bombing, when Egypt was more reluctant than Russia to point to a possible attack. In that case, Egyptian authorities were responsible for security as the city of Sharm el Sheikh was the departure point.

Passengers

EgyptAir said passengers included: 30 Egyptians; 15 French; two Iraqis; one Briton; one Belgian; one Sudanese; one Chadian; one Portuguese; one Algerian; one Canadian; one Saudi and one Kuwaiti. They included a child and two babies.

Seven crew members and three security personnel were also on board.

In Egypt, grieving families and friends are wondering if their loved ones will ever be recovered.

Many have gathered in mosques for Salat al-Ghaib, or "prayers for the absent," held for the dead whose bodies have not been found.

"This is what is ripping our hearts apart, when we think about it," said Sherif al-Metanawi, a childhood friend of the pilot, Mohammed Shoukair. "When someone you love so much dies, at least you have a body to bury. But we have no body."