Wreckage from the EgyptAir flight which crashed in May shows “signs of damage because of high temperature” and a flight data recorder indicated there was smoke on board, investigators said.
The flight from Paris to Cairo crashed into the Mediterranean on May 19 for reasons that remain unknown.
The pilots made no distress call, and no militant group has claimed to have brought down the plane.
The Egyptian investigating committee said in a statement that a recovered flight data recorder, one of the plane’s black boxes, showed that there was smoke in the toilet and onboard equipment.
The second black box, a cockpit recorder, was damaged in the crash and is being repaired in Paris.
The wreckage was recovered from the Mediterranean Sea floor earlier this month. The bulk of the wreckage is believed to be at a depth of about 3,000 metres (9,800 feet).
The committee said deep ocean search teams are still working to find and recover human remains.
French authorities opened a manslaughter inquiry on Monday, but said there is no evidence so far to link the crash to terrorism.
EgyptAir Flight 804 disappeared from radar about 2.45am local time on May 19 between the Greek island of Crete and the Egyptian coast.
Radar data showed the aircraft had been cruising normally in clear skies before it turned 90 degrees left, then a full 360 degrees to the right as it plummeted from 38,000 feet (11,582 metres) to 15,000 feet (4,572 metres).
It disappeared when it was at an altitude of about 10,000 feet (3,048 metres).