The officials, headed by Paul-Louis Arslanian, chief of the French civil aviation ministry's bureau of investigation, said there had appeared to be no problems with the flight before take-off.
Mr Arslanian said there would be no speculation and that it was "essential we check and verify everything".
He said: "This catastrophe - which is the worst that our country has witnessed in terms of aviation, took place in a very difficult region... so the investigation will not be easy... but we are not giving up."
Mr Arslanian said the exact time of the accident was not known, nor whether the chief pilot was at the controls.
Aeronautical engineer Dr Guy Gratton on the search for flight recorders
One French and four Brazilian navy ships are on their way to the area but the Brazilian navy says weather conditions are poor. The flotilla includes divers and a French mini-submarine that can explore to a depth of 6,000m (19,680ft).
French government minister Jean-Louis Borloo said the plane's cockpit voice and data recorders were believed to be at a depth of up to 3,700m (12,100ft), within reach of the submarine, but warned they would be hard to find.
"We have never recovered black boxes that deep before. The sea currents are powerful that far down," he said.
Three merchant vessels are already in the area after being diverted to help with the operation.
Without [the recorders] it will be very difficult to reach established fact, but we can reach a possible explanation
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