An unidentified noise was heard by on-board recorders in the final seconds before a Russian plane crashed in the Sinai Peninsula, Egypt's civil aviation minister said.
Hossam Kamal said the sound was captured by cockpit voice recorders in the moments before the aircraft broke up in mid-air, but the origin is as-yet unknown.
Mr Kamal said that investigators are looking at "all possible scenarios" as to the cause of the crash last Saturday, but confirmed the plane broke up during flight .
The aircraft was flying at 30,888ft and was still gaining altitude when it exploded, 23 minutes and 14 seconds after it left Sharm el-Sheikh airport.
Debris was found scattered over more than 13km, which Mr Kamal said was consistent with a plane breaking up during flight.
The Airbus 321, operated by Russian airline Metrojet, crashed last Saturday, killing all 224 people on board.
Militants of the Islamic State (IS) terror group in the Sinai Peninsula have claimed that they downed the plane.
The wreckage is now being taken to Cairo and investigators, made up of teams from Egypt, Russia, France, Germany and Ireland, as well as advisers from Airbus, will examine it.
Mr Kamal said they were considering all possibilities as to the cause of the in-flight break-up.
He said: "It could be lithium batteries with one of the passengers, it could be an explosion in the fuel compartment - all the scenarios are on the table, I cannot exclude anything."