Rio De Janeiro, Brazil ? The search could not be more daunting — military jets and boats looking for an Air France plane with 228 people aboard that flew beyond the reach of radar and went missing somewhere in the middle of the vast Atlantic Ocean.

Brazilian officials said the area where they think the jet went down is so remote the first military boats will not arrive there until Wednesday morning. Air Force jets from France and Brazil were crisscrossing the ocean Monday, but have yet to spot anything.

Air France Flight 447, a 4-year-old Airbus A330, left Rio Sunday night about 7 p.m. local time with 216 passengers and 12 crew members on board, and flew for more than three uneventful hours before leaving the Brazilian coast. Air traffic controllers lost contact with the jet just as it was entering a band of violent thunderstorms and heavy turbulence that stretched along the equator.

If no survivors are found, it will be the worst air disaster since 2001.

Pilots flying a commercial jet from Paris to Rio de Janeiro for Brazil’s largest airline, TAM, spotted what they thought was fire in the ocean along the Air France jet’s route early Monday, the airline said in a statement e-mailed to The Associated Press.

Brazilian Air Force spokesman Col. Jorge Amaral said authorities were investigating the report, according to the Agencia Brasil official news service.

“There is information that the pilot of a TAM aircraft saw several orange points on the ocean while flying over the region … where the Air France plane disappeared,” Amaral said.

“After arriving in Brazil, the pilot found out about the disappearance (of the Air France plane) and said that he thought those points on the ocean were fire.”

Brazil’s military said its search was focused on a large stretch of ocean 680-745 miles north-northeast of the coastal city of Natal, the area where the plane was when it sent an automated message reporting electrical system failure and a loss of cabin pressure. Three French planes also were en route, and the French navy was asked to send a search craft, a commander said.

The government of France has requested U.S. assistance, said Pentagon spokesman Geoff Morrell, “and we are trying to determine how we can best be of help at this difficult time.”

What happened to the plane remains a mystery and French President Nicolas Sarkozy said “no hypothesis” is being excluded. Some experts dismissed speculation that lightning might have brought the plane down. But violent thunderheads — they reached more than 50,000 feet high in the flight’s path — can pound planes with hail and high winds, causing structural damage if pilots can’t maneuver around them.

The plane was cruising normally at 35,000 feet and 522 mph just before it disappeared nearly four hours into the flight. No trouble was reported as the plane left radar contact, beyond Brazil’s Fernando de Noronha archipelago, at 10:48 p.m. local time.