The plane, which was on its way to Cairo, vanished from radar screens less than an hour after taking off from New York.

Jim Hall, chairman of the US National Transportation Safety Board, described it as a "massive human tragedy" but said that there was no evidence yet of foul play.

EgyptAir said there were 217 people on board including 15 crew, three off-duty employees and two infant passengers.

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It is understood that most of the 199 passengers on board flight 990 were Americans but Egyptians, Sudanese, Syrians and a Chilean were also on the plane.

Coastguards are continuing to search for survivors in a 36 sq mile area of the ocean off the state of Massachusetts.

The BBC's Paul Reynolds: "A massive search is under way for survivors"

Some debris has been found, but only one body has been recovered from the water. The US coastguard said it had found no sign of survivors.

The NSTB, which is leading the crash investigation at the request of the Egyptian Government, has sent its first investigators to set up a command post in Rhode Island.

Mr Hall said: "This is an enormous human tragedy and we want to assure everyone around the world that we will devote all the necessary resources to find out what caused this aircraft to crash.

"We are beginning what may be a long investigation and are prepared to do what it takes to find answers to our questions.

He stressed that, at this early stage of the investigation, it was not known what caused the crash. "Any reports about the cause at this time are pure speculation."

Mr Hall said that flight 990 made routine contact with New York air traffic control at 0147EST (0647 GMT), and reported no problems, just three minutes before it began its descent into the Atlantic.

From cruising at 33,000ft, the plane plunged to 19,100ft in just 36 seconds. "That is a very rapid descent," he said.

American tourists

New York Mayor Rudy Giuliani told a news conference the pasenger list included at least two US tour groups, each containing at least 30 people who were travelling to Egypt for a Nile cruise.

The passengers also included 62 Egyptians, two Sudanese, three Syrians and one Chilean, EgyptAir said. The nationality of the remaining passengers is so far unknown.

Mr Giuliani said Americans on the flight came from across the country including Los Angeles, San Diego and New York.

Arrangements are being made to fly relatives to New York.

Debris located

The search operation is concentrated in a 36 sq mile area south of Nantucket Island, where a ring of debris has been found.

News conference by Jim Hall of the National Transportation Safety Board

The wreckage includes passenger seats, cushions, aircraft flotation devices and two partially inflated life rafts.

US Coast Guard Rear Admiral Richard Larrabee said only one body had so far been recovered. Earlier reports suggested that several bodies had been found in the water.

Four ships and 11 aircraft have joined the search for survivors and any evidence that will help piece together what happened to flight 990.

The FBI is helping with the investigation. But officials said there had been "no threats" and that initial inquiries showed no signs of sabotage.

A Boeing spokesman said this was only the third time that a 767 had been involved in an accident in 17 years of service.

EgyptAir chairman Mohammed Rayan said it was the airline's first fatal crash. The plane, purchased in September 1989, had flown 33,334 hours and had not previously experienced any breakdown, he added.

Friends and relatives wait anxiously at Cairo airport

President Bill Clinton said he was ''very saddened'' by news of the crash .

The 180ft, twin-engined Boeing 767 300, left New York's JFK airport at 0119 EST and was due to arrive in Cairo at 1620 local time (1420 GMT).

US aviation officials in New York said the flight had been delayed for a couple of hours because of its late arrival from Los Angeles. The delay in LA was due to a tyre change.

Relatives' grief

Tearful relatives are at Cairo airport, awaiting further news. Airport officials say the switchboard has been jammed with inquiries.

In New York, crisis counsellors have been sent to help relatives arriving at a hotel near JFK.

The plane's pilot Captain Ahmad al-Habashi was believed to be very experienced with some 10,000 hours flying time.

A BBC Correspondent in Cairo says there has been no hint in local media that the airline was under threat of attack.

EgyptAir Flight 990 was on a route similar to the one taken by Swissair Flight 111, a McDonnell Douglas MD11, which crashed off Nova Scotia on 2 September 1998, killing all 229 people on board.

Planes on that route fly from Kennedy to Nantucket, then turn north to Nova Scotia and Newfoundland before heading east across the Atlantic.

EgyptAir telephone number for concerned relatives is +1 800 243 1094.