Egypt has deployed a submarine to hunt for the black-box flight recorders of the EgyptAir plane that crashed on Thursday in some of the deepest waters of the Mediterranean Sea.
Ships scouring the sea north of Alexandria for three days have found body parts, personal belongings and wreckage from the Airbus A320, but are still trying to locate the recorders that could shed light on the cause of the crash.
The Egyptian president, Abdel Fattah al-Sisi, said all scenarios remained possible.
"So please, it is very important that we do not talk and say there is a specific scenario."
He said the submarine could reach a depth of 3000m.
Sixty-six people were on board the plane when it disappeared from radar en route from Paris to Cairo.
An oil ministry source said the robot submarine was mostly used to maintain offshore oil rigs. It was not clear whether the vessel would be able to help locate the black boxes, or would be used in later stages of the operation.
Air crash investigation experts said the search teams have around 30 days to listen for pings sent out once every second from beacons attached to the two black boxes. At this stage of the search they would typically use acoustic hydrophones, bringing in more advanced robots later to scan the seabed and retrieve any objects once they have been found.
EgyptAir flight 804 from Paris to Cairo vanished off radar screens early on Thursday (local time) as it entered Egyptian airspace over the Mediterranean. The 10 crew and 56 passengers included 30 Egyptian and 15 French nationals.
French investigators said the plane sent a series of warnings indicating that smoke had been detected on board shortly before it disappeared.
The signals did not indicate what caused the smoke or fire, and aviation experts have not ruled out either deliberate sabotage or a technical fault, but they offered early clues as to what unfolded in the moments before the crash.
Anguish of Relatives
EgyptAir has told relatives of the victims that recovering and identifying bodies from the sea could take weeks, adding to the pain and uncertainty of grieving families.
Samar Ezzedine, 27 years old and newly wed, was one of the cabin crew on flight 804. Her mother Amal has sat in the lobby of a hotel overlooking Cairo Airport, still waiting for her daughter to come back.
"She is missing, who hosts a funeral for a missing person?" she murmured.
Samar's aunt, Mona, said Amal was reluctant to go home or even move away from the hotel door. "She doesn't want to believe it... I told her to switch off her phone, but she said: What if Samar calls?"
An EgyptAir union spokesperson appealed to Mr Sisi to allow death certificates to be issued for the victims, to avoid the usual five-year delay in the case of missing people which leaves relatives in a legal limbo, including over pensions.
In his speech on Sunday, Mr Sisi said the investigation would not be over quickly, but promised it would be transparent.
"This could take a long time but no one can hide these things. As soon as the results are out, people will be informed," he told ministers and parliamentarians in the port city of Damietta.
EgyptAir Chairman Safwat Moslem said the radius of the search zone was 40 nautical miles, but could be expanded. The radius is equivalent to an area of 5,000 square nautical miles (17,000 square km).
A European satellite spotted a 2 km-long oil slick in the Mediterranean, about 40 km (20 nautical miles) southeast of the aircraft's last known position, the European Space Agency said.