The pilots spotted two areas of floating debris about 60 kilometers (35 miles) apart, about 410 miles (650 kilometers) beyond the Brazilian island of Fernando de Noronha, roughly along Flight 447's path from Rio de Janeiro to Paris, said Air Force spokesman Jorge Amaral.

"The locations where the objects were found are toward the right of the point where the last signal of the plane was emitted," Amaral said. "That suggests that it might have tried to make a turn, maybe to return to Fernando de Noronha, but that is just a hypothesis."

Amaral said authorities would not be able to confirm that the debris is from the plane until they can retrieve some of it from the ocean for identification. Brazilian military ships are not expected to arrive at the area until Wednesday.

The discovery came more than 24 hours after the jet went missing, with all feared dead.

Rescuers were still scanning a vast sweep of ocean extending from far off North-Eastern Brazil to waters off West Africa. The 4-year-old plane was last heard from at 0214 GMT Monday (10:14 p.m. EDT Sunday). If no survivors are found, it would be the world's worst aviation disaster since 2001.

Investigators on both sides of the ocean are trying to determine what brought the Airbus A330 down, with few clues to go on so far. Potential causes could include violently shifting winds and hail from towering thunderheads, lightning or some combination of other factors.

The crew gave no verbal messages of distress before the crash, but the plane's system sent an automatic message just before it disappeared, reporting lost pressure and electrical failure. The plane's cockpit and "black box" recorders could be thousands of feet (meters) below the surface.

The chance of finding survivors now "is very very small, even nonexistent," said the French minister overseeing transportation, Jean-Louis Borloo. "The race against the clock has begun" to find the plane's two black boxes, which emit signals up to 30 days.” Borloo called the A330 "one of the most reliable planes in the world" and said lightning alone, even from a fierce tropical storm, probably couldn't have brought down the plane.

"There really had to be a succession of extraordinary events to be able to explain this situation," Borloo said on RTL radio Tuesday.

French police were studying passenger lists and maintenance records, and preparing to take DNA from passengers' relatives to help identify any bodies.

France's Defence Minister Herve Morin said "we have no signs so far" of terrorism, but all hypotheses must be studied.

Alain Bouillard, who led the probe into the crash of the Concorde in July 2000, was put in charge of France's accident investigation team.

President Barack Obama told French television stations the United States is ready to do everything necessary to find out what happened.

On board the flight were 61 French citizens, 58 Brazilians, 26 Germans, nine Chinese and nine Italians. A lesser number of citizens from 27 other countries also were on the passenger list, including two Americans.

Among them were three young Irish doctors, returning from two-week vacation in Brazil. Aisling Butler's father John paid tribute to his 26-year-old daughter, from Roscrea, County Tipperary. "She was a truly wonderful, exciting girl. She never flunked an exam in her life - nailed every one of them - and took it all in her stride," he said.

The Airbus A330-200 was cruising normally at 35,000 feet (10,670 meters) and 522 mph (840 kph) just before it disappeared nearly four hours into the flight. No trouble was reported as the plane left radar contact, beyond Brazil's Fernando de Noronha archipelago.

But just north of the equator, a line of towering thunderstorms loomed. Bands of extremely turbulent weather stretched across the Atlantic toward Africa.

France's junior minister for transport, Dominique Bussereau, said the plane sent "a kind of outburst" of automated messages just before it disappeared, "which means something serious happened, as eventually the circuits switched off."

The pilot had 11,000 hours of flying experience, including 1,700 hours flying this aircraft. French Prime Minister Francois Fillon said that if the debris is confirmed to be part of Flight 447, "This will allow us to better determine the search zone."

"We are in a race against the clock in extremely difficult weather conditions and in a zone where depths reach up to 7,000 meters," he told lawmakers in the lower house of French parliament Tuesday.