CAIRO — Body parts, luggage and airplane seats discovered in the Mediterranean Sea on Friday confirmed that EgyptAir Flight 804 crashed into the water but did little to resolve the mystery of what downed the aircraft carrying 66 passengers and crew members.

The first full day of search operations following the Airbus A320 aircraft’s disappearance early Thursday found no sign of the “black box” recorders that could help explain what caused the jet to veer sharply at 37,000 feet before hurtling into the eastern Mediterranean on a clear morning en route from Paris to Cairo.

Egyptian and U.S. officials believe that terrorism, not a mechanical failure, likely brought down the airliner. But no group has claimed responsibility and U.S. intelligence agencies have not identified any passengers or crew members with links to known terrorists, said a U.S. official who spoke on condition of anonymity to discuss internal assessments.

As naval ships and reconnaissance aircraft from the U.S., Egypt and other countries scoured the seas between Greece and Egypt for wreckage, U.S. officials were searching for clues in satellite images and communications collected by intelligence agencies.

Based on radar information showing the airliner abruptly veered 90 degrees to the left before swerving back to the right, officials believe the plane most likely experienced a sudden major structural failure or a bomb blast.

Egyptian President Abdel Fattah el-Sissi urged patience as “investigations are continuing to unravel the circumstances surrounding this unfortunate incident and to establish the truth and the causes of the crash.”

With confirmation that the jet had landed in the sea, el-Sissi expressed “great grief and deep sorrow” for the family members of the 56 passengers, seven crew members and three airline security personnel.

EgyptAir tweeted condolences to the families, saying it “deeply regrets this tragic accident.”

Along with the debris located by the Egyptian armed forces about 180 miles north of the Egyptian coastal city of Alexandria, the European Space Agency detected “a potential oil slick” more than one mile long, about 35 miles southeast of the aircraft’s last known location. While the slick could be jet fuel spilled as the plane broke apart, the agency said there was “no guarantee” it was related to the crash and the satellite would pass over the same area again to gather further images.

The discoveries were helping search teams narrow the focus of their efforts, with the relatively calm waters of the Mediterranean preventing wreckage from drifting far away. A portion of the search area was in some of the deepest reaches of the sea, however, where the waters exceed 10,000 feet in depth.

The U.S. Navy is contributing P-3 Orion submarine-hunting aircraft to the search and recovery effort, Pentagon spokesman Capt. Jeff Davis said. The long-range maritime planes, which fly from Naval Air Station Sigonella in Sicily, are outfitted with advanced radar, electronic sensors and sonar systems.

As the search stretched into Friday evening, Egyptian naval vessels and reconnaissance planes had recovered “passengers’ belongings, body parts, luggage and aircraft seats,” EgyptAir said in a statement.

The Egyptian armed forces, in a statement announcing the earlier discovery of aircraft parts, said “the searching, sweeping and retrieval process is underway.”

Egypt sought to demonstrate it was in control of the investigation a day after EgyptAir said wreckage from the missing plane had been found near the Greek island of Karpathos but later had to retract the statement after Greek officials said the debris did not belong to Flight 804.

The confused messages added to the anguish of family members of victims who had gathered at the Cairo airport and accused the government and airline of mishandling the crisis.

EgyptAir said Friday that Egypt’s civil aviation minister, Sherif Fathi, had appointed an investigative committee, led by Ayman El-Moqadem, the official who also is leading an investigation into a Russian passenger jet that crashed in the Sinai Peninsula last October, killing 224 people on board.

That probe has been criticized in some quarters for failing to produce findings after more than six months of inquiry. The Islamic State, the terrorist organization that has an increasingly active branch in the Sinai, is seen as a possible suspect in the Flight 804 crash because the group claimed to have brought down the Russian jet.

Three French investigators and a technical expert from Airbus arrived in Cairo early Friday to assist in the hunt for Flight 804, airport officials said.

EgyptAir has not issued an official list of passengers, but Egyptian media reported that one town in the northern governorate of Gharbeya said four victims had been born in the area.

Among them was Khaled Allam, 40, who lived in France with his wife and was returning to Egypt from vacation, according to local reports. Another was identified by family members as Haytham Samir Didah, 35, who was living in France with his Moroccan wife and their daughter.

Of the 56 passengers aboard, 30 were Egyptians, 15 were from France and two from Iraq. There were also passengers from Britain, Belgium, Saudi Arabia, Sudan, Chad, Portugal, Algeria, Kuwait and Canada.

EgyptAir identified the pilot as Mohamed Shokair and his copilot as Mohamed Assem. Shokair had 6,275 flying hours under his belt, the airline said, including more than 2,000 on the Airbus A320, one of the most common passenger aircraft in the world.

(Los Angeles Times staff writer Bengali and special correspondent Hassan reported from Cairo, and staff writer Bennett from Washington. Staff writer W.J. Hennigan in Washington contributed to this report.)

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