Minutes before EgyptAir Flight 804 plunged into the Mediterranean Sea early Thursday, smoke alarms rang out in the plane’s cabin, according to flight data.
The Aviation Herald website, which covers the aviation industry, published data that shows smoke alarms in the bathroom ringing out not long before the plane crashed.
The Aviation Herald reported that it received the information via the Aircraft Communications Addressing and Reporting System (ACARS), a system used by airline operators to download flight data, which shows that smoke was detected in the toilet at 2:26 a.m. local time.
About a minute later, another alarm went off signaling an avionics smoke alert.
Then, two minutes later, the last ACARS alert went out signaling smoke or a fire near the electronics and equipment bay of the aircraft.
France's aviation safety agency confirmed the validity of the messages, but a spokesman said it is "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."
Egyptian authorities are also investigating the smoke alerts.
Search crews have found human remains along with the personal belongings of passengers from the aircraft but are still searching for the bulk of the wreckage.
Looking for clues to understand why the jet carrying 66 people crashed into the Mediterranean Sea, search teams sought to find larger pieces of the plane or the location signal from the flight recorders.
Egypt Aviation Minister Sherif Fathy has said a terrorist attack is a more likely cause for the crash than technical failure. But so far no clear evidence has emerged as to what brought the plane down.
No militant group has claimed to have carried out an attack.
The plane disappeared into the Mediterranean Sea, north of the Egyptian coast, early Thursday while headed to Cairo from Paris.
The Airbus A320 had been flying normally when it suddenly swerved radically and plunged more than 11,000 meters into the sea, never issuing a distress signal.
The European Space Agency said one of its orbiting spacecraft spotted what could be an oil slick 40 kilometers southeast of the plane's last known position and the information had been passed on to relevant authorities conducting a search mission.
The agency released a grainy photograph of the scene that showed little detail and cautioned there was no certainty the slick was from the aircraft.
The ESA said a second satellite would on Sunday pass the area where the slick was found.
Three French investigators and a technical expert from the A320's manufacturer, Airbus, arrived Friday in Cairo to aid in the investigation.
U.S. Secretary of State John Kerry offered Egypt continued support for the search.
Kerry offered condolences to Egyptian Foreign Minister Sameh Shoukry for the lives lost on the flight, and said the United States would stay in close contact as the investigation progressed.
Egypt, France, Greece and the U.S. are among nations deploying planes and naval vessels to search for the plane.
WATCH: Prayers for EgyptAir crash victims
Prayers and a symbolic funeral for the passengers were held Friday at Cairo's Sultan Hussein Mosque.
EgyptAir sent interpreters and doctors to the Cairo airport to meet with the passengers' families.
The disappearance has renewed security concerns months after a Russian passenger plane was shot down over the Sinai Peninsula.
The Russian aircraft crashed in Sinai on October 31, killing all 224 people on board. Moscow said it was brought down by an explosive device, and a local branch of the extremist Islamic State group claimed responsibility for planting it.