CAIRO -- An EgyptAir jetliner en route from Paris to Cairo with 66 people aboard swerved wildly in flight and crashed in the Mediterranean Sea early Thursday, authorities said. Egyptian and Russian officials said it may have been brought down by terrorists.
There were no signs of survivors.
EgyptAir Flight MS804, an Airbus A320 with 56 passengers and 10 crew members, went down about halfway between the Greek island of Crete and Egypt's coastline, or around 175 miles offshore, after takeoff from Charles de Gaulle Airport, authorities said.
A U.S. intelligence source said all indications are that a catastrophic event took down the airplane, CBS News senior investigative producer Pat Milton reports. Investigators believe that in part because of the aircraft's flight path and the high rate of speed of its descent.
The source said indications are that the aircraft fell like a rock, Milton reports.
The source said investigators do not know whether the crash was caused by a deliberate act, such as a bomb, or mechanical failure, Milton reports.
Numerous types of explosive devices are being considered, including a bomb with a timing device, an altitude device or one that was set off inside the passenger cabin by a suicide bomber on the flight.
A U.S. official said no sign of an explosion was detected, CBS News national security correspondent David Martin reports.
The data from an infrared satellite doesn't rule out the possibility that one occurred, since the satellite was not calibrated to detect explosions over the Mediterranean.
U.S. intelligence and law enforcement have been searching for signs of a claim of responsibility or "chatter" from the Islamic State of Iraq and Syria, or ISIS, but so far there have not been any obvious signs, CBS News homeland security correspondent Jeff Pegues reports.
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. Cairo 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. There were no reports of stormy weather at the time.
Egyptian and Greek authorities in ships and planes searched the suspected crash area throughout the day for traces of the plane, with help on the way from various other countries.
But as night fell, the searchers had yet to find any confirmed debris, at one point dismissing a reported sighting of life vests and other floating material.
Civil Aviation Minister Sherif Fathi cautioned that the disaster was still under investigation but 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, went further, saying: "In all likelihood it was a terror attack."
If it was terrorism, it would be the second deadly attack involving Egypt's aviation industry in seven months.
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 ISIS claimed responsibility.
Thursday's disaster also raises questions about security at De Gaulle Airport, at a time when Western Europe has been on high alert over the deadly Islamic extremist attacks in Paris and at the Brussels airport and subway over the past six months.
In the past day, the plane had flown to Eritrea, to Tunisia and then to Paris. An explosive device on a timer could have been loaded anywhere, according to CBS News transportation security analyst and former NTSB chairman Mark Rosenker.
"That's why the investigators are going to be looking at all of the stops that this aircraft made prior to coming to Paris," Rosenker said. "They're going to make a very serious examination and series of interviews with anybody that had any kind of exposure to this aircraft -- whether it was cleaning crew, whether it was catering crew, whether it was the refueling crew or whether it was the baggage crew."
The airline said there were three security personnel on the flight when it left Paris, which it called routine.
CBS News correspondent Mark Phillips notes that French authorities have tightened airline security since the attacks on Paris. Not only passengers, but anyone who gets near a plane in the French capital goes through screening, and people have been dismissed for security reasons.
The big question now, says Phillips, is whether somewhere -- be it in France, Egypt or Tunisia -- security measures failed.
French Foreign Minister Jean-Marc Ayrault said that airport security had been tightened considerably before the disaster, in particular because of the coming European soccer championship, which France is hosting.
The plane's erratic course raised a number of possibilities, including a catastrophic mechanical or structural failure, a bombing, 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.
Law enforcement sources told CBS News the FBI would offer assistance to investigators in the crash. The FBI is known to have some of the most skilled bomb technicians on the planet, and their dive teams and evidence response teams are also among the best, Pegues reports.
"Right now we have to find where this aircraft is," Rosenker told CBS News, explaining that once that was accomplished, the focus of the search would turn quickly to the plane's flight data and cockpit voice recorders -- the so-called "black boxes." Those instruments should contain information to help investigators determine what brought the plane down.
Rosenker noted that whatever caused the plane to disappear happened at cruising altitude -- about 37,000 feet -- and "very, very few accidents occur at that altitude, about 10 percent."
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.
Capt. Chesley "Sully" Sullenberger, CBS News aviation consultant and "Miracle on the Hudson" pilot, said the lack of a distress call from the flight crew suggests a likely catastrophe in the air.
"Something must have happened that either prevented the pilots from communicating or made them so busy that they couldn't get to a priority as low as talking on the radio. They were trying to maintain control of the airplane or fight a sudden catastrophic emergency, for example," Sullenberger said on "CBS This Morning."
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, an accidental structural failure aboard the highly reliable A320 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 and various governments, 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 two Canadians. The passengers included two babies.
Among the passengers, according to employers and officials, were the Egypt-raised manager of a Procter & Gamble plant in Amiens, France; a Saudi woman who works at the Saudi Embassy in Cairo; the sister-in-law of an Egyptian diplomatic official in Paris; and a student at France's prestigious Saint-Cyr military academy who was heading to home to Chad to mourn his mother.
Whatever caused the crash, the disaster is likely to deepen Egypt's woes as the country struggles to revive its ailing economy, particularly its lucrative tourism industry. It has been battered by the bloodshed and political turmoil in which the country has been mired since the 2011 overthrow of President Hosni Mubarak.
French and British authorities joined the search-and-rescue operation. France also sent a team of accident investigators.
A U.S. Navy P-3 Orion surveillance plane from Naval Air Station Sigonella on Sicily was to join the search effort south of Greece, American military officials told CBS News.
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 and 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.
Families of passengers gathered at the Cairo airport, desperate for any news. Authorities brought doctors to the scene after several distressed family members collapsed.
"They don't have any information," lamented Mohamed Ramez, whose in-laws were on the plane. "But obviously there is little hope."
At De Gaulle Airport, a man and woman sat at an information desk near the EgyptAir counter, the woman sobbing into a handkerchief, before they 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.