Human remains retrieved from the EgyptAir Flight 804 crash site point to an explosion on board, according to an Egyptian forensic official.
The official said that the "logical explanation is that an explosion" brought down the aircraft in the east Mediterranean, The Associated Press reports.
The official is part of the Egyptian team investigating the crash that killed 66 people on board the flight travelling from Paris to Cairo on Thursday.
He has personally examined the remains at a Cairo morgue and spoke on condition of anonymity because he was not authorised to release the information.
All 80 pieces that have been brought to Cairo so far are small.
"There isn't even a whole body part, like an arm or a head," said the official, adding that one piece was the left part of a head.
"But I cannot say what caused the blast," he added.
The first pictures of debris from the plane were released on Saturday.
Images showed what appeared to be part of a seat, as well as a life jacket.
On Monday it emerged that the aircraft had “we will bring this plane down” scrawled on the side of it in Arabic.
Political activists who worked at Cairo Airport were said to be behind the graffiti, written on the underside of the jet about two years ago.
Others also wrote “murderer” and “traitor” in messages directed at Egypt’s president Abdel Fattah el-Sisi, The New York Times revealed following interviews with three separate EgyptAir security officials.
The new report directly contradicts official accounts of the crash by the investigating authorities, which state no such call was made.
The Airbus A320 was en-route from Charles de Gaulle airport in France to Cairo, when contact was lost around 12:45am about 10 miles into Egyptian airspace.
Experts believe the crash was most likely the result of a terrorist attack.
Briton Richard Osman, a father-of-two originally from Wales, is among 56 passenger and 10 crew thought to have died in the crash.
EgyptAir is said to have introduced a series of security measures in response to the political turmoil and other plane disasters like the Metrojet plane that was downed after taking off from Sharm el-Sheikh Airport, killing all 224 people on board.
The head of the Egyptian investigation team, Ayman al-Moqadem, said on Sunday that it will take four weeks for information to be compiled and published as pictures of recovered debris began to circulate.
Meanwhile, French investigators, who are assisting the official inquiry, have revealed the jet sent a series of warnings before it disappeared off radar just before 2.30am.
The signals indicated smoke or fire had been detected on board. While not dismissing these reports, officials have warned the public not to read too much into the claims until the black box has been recovered.