Greek Defense Minister Panos Kammenos said the plane spun all the way around and suddenly lost altitude just before vanishing from radar screens around 2:45 a.m. Egyptian time.
He said it made a 90-degree left turn, then a full 360-degree turn toward the right, plummeting from 38,000 to 15,000 feet. It disappeared at about 10,000 feet, he said.
An Egyptian search plane later located two orange items believed to be from the aircraft, 230 miles southeast of Crete, a Greek military official said, speaking on condition of anonymity in accordance with regulations.
In Cairo, Egyptian Civil Aviation Minister Sherif Fathi cautioned that the disaster was still under investigation, but he said the possibility it was a terror attack "is higher than the possibility of having a technical failure."
Alexander Bortnikov, chief of Russia's top domestic security agency, said: "In all likelihood it was a terror attack."
The Egyptian military said it did not receive a distress call, and Egypt's state-run daily Al-Ahram quoted an unidentified airport official as saying the pilot did not send one. The absence of a distress call suggests that whatever sent the aircraft plummeting into the sea was sudden and brief.
The plane's erratic course suggested a number of possibilities, including some kind of catastrophic mechanical or structural failure — whether accidental or the result of sabotage — or a struggle over the controls with a hijacker in the cockpit.
Egyptian security officials said they were running background checks on the passengers to see if any had links to extremists.
The disaster also raises questions about security at De Gaulle Airport, at a time when Western Europe is on edge over the deadly Islamic extremist attacks in Paris and at the Brussels airport and subway over the past six months.
French Foreign Minister Jean-Marc Ayrault said that airport security had been toughened considerably before the disaster, in particular because of the coming European soccer championship, which France is hosting.
Last October, a Russian passenger plane that took off from an Egyptian Red Sea resort crashed in the Sinai, killing all 224 people aboard. Russia said it was brought down by a bomb, and a local branch of the Islamic State claimed responsibility.
Retired U.S. Air Force Maj. Gen. Robert Latiff, an expert on aerospace systems at the University of Notre Dame, said that while it is too early to tell for certain, a structural failure aboard the plane is "vanishingly improbable."
He also cast doubt on the possibility of a struggle in the cockpit, saying the crew would have triggered an alarm.
Instead, he said, "sabotage is possible, and if there were lax controls at airports and loose hiring and security policies, increasingly likely."
Those on board, according to EgyptAir, included 15 French passengers, 30 Egyptians, two Iraqis, one Briton, one Kuwaiti, one Saudi, one Sudanese, one Chadian, one Portuguese, one Belgian, one Algerian and one Canadian.
Egyptian military aircraft and ships searched for debris and victims from the plane, whose passengers included two babies and a child, officials said. Greek, French and British authorities joined the operation.
Whatever caused the crash, the disaster is likely to deepen Egypt's woes as the country struggles to revive its ailing economy, particularly the lucrative tourism sector that has been battered by the turmoil in which the country has been mired since a 2011 popular uprising.
The crash also renewed security concerns surrounding Egyptian planes and airports. A Russian passenger plane crashed in the Sinai last October, killing all 224 people aboard. Moscow said the aircraft was brought down by a bomb, and a local branch of the Islamic State claimed responsibility.
French President Francois Hollande held an emergency meeting at the Elysee Palace. He also spoke with Egyptian President Abdel-Fattah el-Sissi by telephone and agreed to "closely cooperate to establish as soon as possible the circumstances" surrounding the disaster, according to a statement.
In Cairo, el-Sissi convened an emergency meeting of the National Security Council, the country's highest security body. It includes the defense, foreign and interior ministers, in addition to the chiefs of the intelligence agencies.
In Paris, the city prosecutor's office opened an investigation. "No hypothesis is favored or ruled out at this stage," it said in a statement.
About 15 relatives of passengers arrived at the Cairo airport, and authorities brought doctors to the scene after several distressed family members collapsed.
In Paris, relatives started arriving at De Gaulle Airport outside the French capital.
A man and a woman, identified by airport staff as relatives of passengers, sat at an information desk near the EgyptAir counter. The woman sobbed, holding her face in a handkerchief. The pair were led away by police.
The Airbus A320 is a widely used twin-engine plane that operates on short and medium-haul routes. Nearly 4,000 A320s are in use around the world.
The last deadly crash involving one of the planes was in March 2015, when one of the pilots of a Germanwings flight deliberately slammed it into the French Alps, killing all 150 people aboard.
Airbus said the aircraft in Thursday's disaster was delivered to EgyptAir in 2003 and had logged 48,000 flight hours. The pilot had more than 6,000 hours of flying time, authorities said.
In March, an EgyptAir plane was hijacked and diverted to Cyprus. A man described by authorities as mentally unstable was taken into custody.
