PARIS — France's transportation minister said Friday that French forces have found no signs of the Airbus A330 jet that vanished over the Atlantic and urged "extreme prudence" about suspected debris taken from the ocean.

Dominique Bussereau said he regretted that an announcement by Brazilian teams that they had recovered plane debris from Air France flight 447 turned out to be false.

The Brazilian air force announced Thursday afternoon that a helicopter plucked an airplane cargo pallet from the sea that came from the Air France flight, but then said six hours later that it was not from the Airbus.

"French authorities have been saying for several days that we have to be extremely prudent," Bussereau said. "Our planes and naval ships have seen nothing."

Bussereau said the search must continue and stressed that the priority was finding the flight recorders. The plane went down Sunday night with 228 people on board in the world's worst aviation disaster since 2001.

France's defense minister and the Pentagon have said there were no signs that terrorism was involved. Brazil's defense minister said the possibility was never considered.

French Foreign Minister Bernard Kouchner, speaking Thursday in Rio de Janeiro where he attended a Mass honoring the crash victims, said experts had not found signs that would back up a "terrorism theory."

Investigators are looking into whether malfunctions in instruments used to determine airspeed may have led the plane to be traveling at the wrong speed when it encountered turbulence from towering thunderstorms over the Atlantic Ocean.

Two aviation industry officials told The Associated Press on Thursday that investigators were studying the possibility that an external probe that measures air pressure may have iced over. The probe feeds data used to calculate air speed and altitude to onboard computers. Another possibility is that sensors inside the aircraft reading the data malfunctioned.

If the instruments were not reporting accurate information, the jet could have been traveling too fast or too slow as it hit turbulence from violent thunderstorms, according to the officials.

But Gerard Feldzer, a former Air France pilot, cautioned against drawing conclusions about the crash.

"We don't know whether there was depressurization. Perhaps a quarter of an hour later it was resolved and it (the cause of the crash) was something completely different."