The EgyptAir jet which crashed in the Mediterranean on Thursday sent a series of warnings indicating that smoke had been detected on board, shortly before it disappeared off radar screens, French investigators said on Saturday.
A spokesman for France's BEA air accident investigation agency said the signals did not indicate what caused the smoke or fire on board the plane, which plunged into the sea with 66 people on board as it was heading from Paris to Cairo.
But they offered the first clues as to what unfolded in the moments before the crash.
One aviation source said that a fire on board would likely have generated multiple warning signals, while a sudden explosion may not have generated any - though officials stress that no scenario, including explosion, is being ruled out.
Egypt said its navy had found human remains, wreckage and the personal belongings of passengers floating in the Mediterranean about 290 km (180 miles) north of Alexandria.
The army published pictures on Saturday on its official Facebook page of the recovered items, which included blue and white debris with EgyptAir markings, seat fabric with designs in the airline's colors, and a yellow lifejacket.
Analysis of the debris and recovery of the plane's twin flight recorders are likely to be key to determining the cause of the crash - the third blow since October to Egypt's travel industry, still reeling from political unrest following the 2011 uprising that ousted Hosni Mubarak.
A suspected Islamic State bombing brought down a Russian airliner after it took off from Sharm el-Sheikh airport in late October, killing all 224 people on board, and an EgyptAir plane was hijacked in March by a man wearing a fake suicide belt.
A message purporting to come from Islamic State urged attacks on the United States and Europe in the Islamic holy month of Ramadan beginning in early June. "Ramadan, the month of conquest. Get prepared...so that you make it a month of calamity on the non-believers anywhere," said the message posted on Twitter accounts that usually publish Islamic State statements.
It made no claim of responsibility for the Egyptair crash.
The October crash devastated Egyptian tourism, a main source of foreign exchange for a country of 80 million people, and another similar incident would crush hopes of it recovering.
Egypt's tourism revenue in the first three months of the year plunged by two thirds to $500 million from a year earlier.
HUNT FOR BLACK BOXES
The signals from the plane "do not allow in any way to say what may have caused smoke or fire on board the aircraft", said a spokesman for the French BEA agency, which is assisting an official Egyptian investigation.
He added that the priority now was to find the two flight recorders, known as black boxes, containing cockpit voice recordings and data readings, from the Airbus A320 which vanished from radar early on Thursday.
Egyptian said it was too soon to reach any conclusions about the cause of the crash.
Civil Aviation Minister Sherif Fathi told reporters an additional challenge in the hunt for the black boxes was the depth of the Mediterranean in the area under search. "What I understand is that it is 3,000 (meters)," he said.
That would place the black box locator beacons, which last for 30 days, on the edge of their detectable range from the surface based on the type of acoustic equipment typically used during the first stages of a search, according to a report into the 2009 crash of an Air France jet in the Atlantic.