Air France 447 - More debris found from Air France plane crash
RIO DE JANEIRO, Brazil (CNN) -- Searchers found four more debris fields Wednesday from an Air France jet that plunged into the Atlantic Ocean early Monday with 228 people on board, the Brazilian Air Force said.
Image released by the Brazilian Air Force shows oil slicks in the water near a debris site.
The Airbus A330 went down about three hours after beginning what was to have been an 11-hour flight from Rio de Janeiro to Paris, France.
Investigators have not determined what caused the plane to crash. The flight data recorders have not been recovered and the plane's crew did not send any messages indicating problems before the plane disappeared. 
Watch as high seas hamper recovery »
The aircraft's computer system did send about four minutes of automated messages indicating a loss of cabin pressure and an electrical failure, officials have said.
Some investigators have noted that the plane flew through a severe lightning storm. Foul play has not been ruled out.
Air France had received a bomb threat May 27 for a flight from Buenos Aires, Argentina, to Paris, sources in the Argentine military and police told CNN on Wednesday.
According to the officials, who had been briefed on the incident and declined to be identified because of the ongoing investigation, the Air France office in Buenos Aires received the threat from a man speaking Spanish.
Authorities checked the Boeing 777 and did not find anything. Security was tightened during check-in for Flight 415, which left on time and without incident, the officials said.
Among the debris found Wednesday were various objects in a circular 5-kilometer (3-mile) area; one object with a diameter of 7 meters (23 feet); 10 objects, some of which were metallic; and a thin oil slick that extended as far as 20 kilometers (12 miles), said Brazilian Air Force spokesman Jorge Amaral.
The latest debris was found about 90 kilometers (56 miles) south of Tuesday's discovery, Amaral said. The earlier debris was about 650 kilometers (400 miles) northeast of the Fernando de Noronha Islands, an archipelago 355 kilometers (220 miles) off the northeast coast of Brazil. 
Map of Flight AF 447's flightpath »
The wreckage found Tuesday included an aeroplane seat, metal debris, an orange float, a drum and an oil spill.
Eleven aircraft and five ships are engaged in the search, including airplanes from France and the United States. Watch as experts question whether recovery is possible »
Although officials have said the likelihood of finding survivors are small, authorities have not closed the door on the possibility.
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"Until the aircraft is identified, and the remains indicate that survival is technically impossible, we will maintain the possibility that there could be survivors," Amaral said.
The majority of the people on the flight came from Brazil, France and Germany. The remaining victims were from 29 other countries, including three passengers from the United States.
French officials said Wednesday they may never find the jet's flight data recorders.
"We need time to reach the recorders," said Paul-Louis Arslanian, head of France's accident investigation bureau.
The recorders give off a locator signal that lasts for up to 30 days. The French government has sent a research vessel with a deep-diving submersible on board to the area where the debris was found.
French officials said weather conditions at the site remain "extremely difficult" and the depth of the Atlantic near the area where wreckage was found is around 7,000 meters (21,000 feet).
"Even in history ... recorders from time to time were found after the 30 days. But I'm not so optimistic," Arslanian said. "It's not only deep, it's also very mountainous at that place of the ocean."
Brazilian officials have said the sea depth in the area is around 2,000 to 3,000 meters (6,562 to 9,842 feet).
Brazilian President Luis Inacio Lula da Silva was optimistic that the flight data recorders would be found.
"I think that a country with the ability to retrieve oil from 6,000 meters (3.7 miles) underwater can retrieve a plane from 2,000 meters (1.2 miles). The truth is, we are going to see -- I'm not a specialist and don't want to give predictions of what will happen," Lula said, according to the Brazilian state news agency.
Arslanian said answers on what caused the crash could take a long time.
"It could be long, we cannot do with 80 percent understanding," he said. "This catastrophe is the worst that our country has known in our country's air history."
A memorial for the victims of Flight AF 447, which included 61 people from France, 58 Brazilians, 26 Germans and people from 29 other countries, took place later Wednesday at the Notre Dame Cathedral in Paris. Brazil has declared three days of mourning.
