An intense sea operation to find the remains of an Air France jet that plunged into the Atlantic this week was being bolstered after days of fruitless searching, officials said, AFP reported.
A French nuclear submarine was on its way to the zone, 1,000 kilometers (600 miles) off Brazil's northeast coast, to help look for the black boxes from flight AF 447 which was lost Monday as it flew from Rio de Janeiro to Paris with 228 people on board.
Two more Brazilian navy vessels late Friday were also to join three others already in the area, which was being overflown by 12 Brazilian and French aircraft.
The head of air traffic control for the area, Brazilian Brigadier Ramon Cardoso, told reporters "we have not made any recovery of material."
Some items spotted floating in the vicinity were "not relevant," he said, adding that weather conditions were terrible, limiting visibility, and currents had changed direction.
Brazilian officials said items picked up Thursday turned out on closer inspection to be nothing more than trash, probably from ships.
But positive sightings in the waves of a seat from a plane and cables and other components on Tuesday and Wednesday convinced searchers they were in the right spot.
Cardoso said those objects might have since sunk to the bottom of the ocean, where the plane's black boxes are also believed to be.
Without clues from the wreckage or the data in the black boxes, speculation climbed over what caused the accident.
French Defense Minister Herve Morin told reporters in Paris he had not ruled out a terrorist attack on the plane, although he had not heard of any threats or claims of responsibility being made.
French Transport Minister Dominique Bussereau said "we must do everything we can to find the flight recorders" but admitted "time is against us."
Plane-maker Airbus had issued a notice warning crews on its aircraft worldwide what to do when speed indicators give conflicting read-outs, suggesting a link with data alerts sent by the ill-fated Air France plane shortly before it met its end.
According to David Learmont, editor in chief of Flight International, the decision to issue the warning does not mean that investigators know what happened, but that they had seen similar situations in the past.
"What Airbus is saying is, 'Whatever happened to these pilots, they didn't manage to handle it. We don't know everything that they faced but we know a little bit about the nature of the situation they faced'," he told AFP.
"So all they've done is that they've gone back to the airlines and the pilots and said: have a quick look at this, because it might save your life."
While the investigation cast about for clues, families of those on board the plane expressed frustration with the lack of physical evidence that their loved ones were gone forever.
A group of 10 Brazilian relatives were flown from Rio to the main search operations center in the Brazilian city of Recife on Friday to speak to a pilot involved in the search for the plane.
They left without speaking to media, and returned to Rio where another service was held in memory of the Air France passengers and crew.
Meanwhile, Rio's attorneys association blasted "harassment" of the relatives by Brazilian and foreign lawyers smelling a lucrative lawsuit in the tragedy.
Any Brazilian lawyer caught trying to sign up the grieving kin would be punished, it warned, while saying any foreign lawyer who had entered the country on a tourist visa and was trying to drum up business was breaking the law.
"A lawyer is not a vulture who goes after human pain," said the head of the association, Wadih Damous.
Also in Rio, police began collecting genetic samples from relatives of the passengers on the doomed flight in order to accelerate the identification process should any remains from the crash be found.