THE attempted terrorist attack on a Christmas Day flight began with a pop and a puff of smoke - sending passengers scrambling to subdue a man who claimed to be acting on orders from al-Qaida, officials and travellers said.

The commotion began as Northwest Airlines Flight 253, carrying 278 passengers and 11 crew members from Amsterdam, prepared to land in Detroit.

"It sounded like a firecracker in a pillowcase," said Peter Smith, a passenger from the Netherlands. "First there was a pop, and then (there) was smoke."

Smith said one passenger climbed over other passengers, went across the aisle and tried to restrain the alleged attacker. The heroic passenger appeared to have been burned.

Afterward, the suspect was taken to a front-row seat with his pants cut off and his legs burned. Multiple law enforcement officials also said the man appeared badly burned on his legs, indicating the explosive was strapped there. The components were apparently mixed in-flight and included a powdery substance, officials said.

The suspect is studying at a UK university, it was reported yesterday.

The Nigerian is accused of trying to detonate a powdery substance on a plane from Amsterdam as it prepared to land at Detroit with 278 people on board.

He has been named by ABC News as Abdul Farouk Abdulmutallab, 23, an engineering student at University College London, with the broadcaster citing US government documents.

The suspect, who has also been identified as Umar Farouk Abdul Mutallab in other reports, is under guard at a Michigan hospital.

Religious ceremony

He was flying from Nigeria to the United States for a religious ceremony according to his entry visa, ABC News said, which was issued on 16 June last year and valid until June 12, 2010.The White House said it believed it was an attempted act of terrorism and stricter security measures were quickly imposed on airline travel. The incident was reminiscent of Richard Reid, who tried to destroy a trans-Atlantic flight in 2001 with explosives hidden in his shoes, but was subdued by other passengers.

Multiple law enforcement officials identified the suspect in Friday's attempted attack as Umar Farouk Abdul Mutallab. He was described as a Nigerian.

One law enforcement official said the man claimed to have been instructed by al-Qaida to detonate the plane over US soil, but other law enforcement officials cautioned that such claims could not be verified immediately, and said the man may have been acting independently - inspired but not specifically trained or ordered by terror groups.

All the officials spoke on condition of anonymity because the investigation was continuing.

Melinda Dennis, who was seated in the front row of the plane, said the man involved was brought to the front row and seated near her. She said his legs appeared to be badly burned and his pants were cut off. She said he was taken off the plane handcuffed to a stretcher.

One law enforcement official said Mutallab's name had surfaced earlier on at least one US intelligence database, but not to the extent that he was placed on a watch list or a no-fly list.

The flight began in Nigeria and went through Amsterdam en route to Detroit, said Peter King, the ranking Republican member of the House Homeland Security Committee. A spokeswoman for police at the Schiphol airport in Amsterdam declined comment about the case or about security procedures at the airport for Flight 253.

A spokesman for the Federal Airports Authority of Nigeria, Akin Olunkunle, said all passengers and their luggage are screened before boarding international flights. He also said the airport in Lagos cleared a US Transportation Security Administration audit in November.

Delta Air Lines Inc, which acquired Northwest last year, said a passenger caused a disturbance, was subdued, and the crew requested that law enforcement officials meet the flight.

Passenger Syed Jafri, a US citizen who had flown from the United Arab Emirates, said the incident occurred during the plane's descent. Jafri said he was seated three rows behind the passenger and said he saw a glow, and noticed a smoke smell. Then, he said, "a young man behind me jumped on him".

"Next thing you know, there was a lot of panic," he said.

Federal officials said there would be heightened security for both domestic and international flights at airports across the country, but the intensified levels would likely be "layered," differing from location to location depending on alerts, security concerns and other factors.

Passengers can expect to see heightened screening, more bomb-sniffing dogs and officer units and behavioural-detection specialists at some airports, but there will also be unspecified less visible precautions as well.

The FBI and the Homeland Security Department issued an intelligence note on 20 November about the threat picture for the holiday season. At the time, officials said they had no specific information about attack plans by al-Qaida or other terrorists.

President Barack Obama was notified of the incident and is monitoring the situation and receiving regular updates from his holiday in Hawaii.

Installing the type of security at airports to combat terrorism of the kind attempted on the Detroit-bound flight could be extremely costly and take a very long time, aviation experts said.

It would need a whole new set of equipment which would have to be acquired at great cost and then installed at airports, said aviation expert Kieran Daly. "The global task of getting that equipment installed will be very, very difficult within the sort of timescale that is required."

Increased security

However he added that the attempted attack was, in a sense, "not all bad news". Daly went on: "The latest incident could in some respects be described as a success in that it shows that would-be terrorists are now having to resort to trying to get very small devices onboard planes.

"Thanks to increased security, the sort of devices are now not big enough to actually bring down a plane. The terrorists have had to resort to more and more inadequate devices and they are a very long way from actually bringing down an aircraft."

Daly said that security was also being helped by the fact that terrorists, seeking maximum publicity and impact, were concentrating on the very airport and routes where security was actually at its most efficient.