Even as search efforts have intensified in the hunt for an Air France jet that disappeared over the Atlantic with 228 people on board, relatives have apparently been told that the chances of finding survivors are "very slim."
Authorities are still trying to determine what caused the accident.
French president, Nicolas Sarkozy, told waiting relatives at the Charles de Gaulle airport in Paris that "the prospects of finding any survivors are very slim".
"It's a catastrophe the likes of which Air France has never seen," he added.
If confirmed, then the loss of 228 people would be civil aviation's worst accident for more than a decade. Air France said the 216 passengers hailed from 32 countries and comprised 126 men, 82 women, seven children and a baby. There were also 12 French crew members on board.
Meanwhile, a spokesman for Brazil's air force has been quoted by the official Agencia Brasil news agency as saying that a commercial aircraft pilot had spotted what appeared to be fireballs in the Atlantic along the route of the missing Airbus A330-200 jet. The location apparently matches the area where the missing Flight AF447, flying from Rio de Janeiro in Brazil to Paris, France, disappeared from radar screens.
The search involves an area more than 1,100km off the Brazilian coast. Current search efforts are primarily aircraft based with the first naval vessels expected to arrive only on Wednesday.
The A330 was about 230 miles northeast of the Brazilian coast approaching heavy thunderstorms which experts say are typical phenomena at the intertropical convergence zone (ITCZ) at that latitude.
The ITCZ is an area of continuous low pressure that lines the equatorial regions.
It is now clear that Flight AF447 encountered a severe thunderstorm and that the aircraft sent an automated message saying that its electrical system had failed.
Pierre-Henry Gourgeon, Air France's chief executive, said "several electrical systems had broken down".
Air France said the pilots were very experienced. The A330 aircraft has a good safety record.
The United States, too, has joined the hunt for the missing aircraft with the Pentagon confirming Monday it had dispatched a surveillance aircraft and a search and rescue team.
France has also asked Washington to scan data from its spy satellites and electronic intelligence facilities for clues.
US Air Force Defense Support Program (DSP) missile warning satellite data, collected early 1 June over the central Atlantic, will be examined to see if a breakup or impact of a crashing aircraft was captured.
Experts say two or three Northrop Grumman DSPs constantly scan that region of the Earth with powerful infrared telescopes. The satellites, based in geosynchronous orbit at nearly 23,000 miles in altitude, are designed to detect the heat from the launch of land or sea based ballistic missiles.
Each satellite carries a 6,000 element mercury-cadmium-telluride detector which is capable of discriminating not only missile launches but other thermal phenomenon such as lightning, meteorites and aircraft that are flying on afterburner or on fire.
Other systems being tapped for data will include two new Space Based Infrared System (SBIRS) sensors onboard two National Reconnaissance Office spacecraft in highly elliptical orbits. Unlike DSPs, the new SBIRS satellites are yet to provide continual coverage of all areas of Earth. It remains to be seen if a SBIRS system was pointing in the area of the crash.
SIGINT (signal intelligence) "eavesdropping" spacecraft data will also be examined for unusual static or other transmissions which may have been picked up coming from the stricken aircraft.