Security forces enter the plane

Passengers on the Delta airlines flight to the US helped subdue a Nigerian man after they smelled smoke and heard the noise of firecrackers going off, it emerged yesterday.

Flight 253 from Amsterdam was about 20 minutes outside Detroit when passengers heard popping noises. At least one passenger climbed over other people and jumped on the man, witnesses said.

A short time afterwards the suspect, an engineering student at University College London later named as Umar Farouk Abdul Mutallab (23), was brought to the front of the plane. The legs of his trousers had been cut short and his legs appeared to have suffered extensive burns, indicating that the explosive material had been strapped to them.

One US intelligence official said the explosive device was a mix of powder and liquid. It failed when the passenger tried to detonate it.

"It sounded like a firecracker in a pillowcase," said Peter Smith, a traveler from the Netherlands. "First there was a pop, and then smoke." Smith said a passenger sitting opposite the man climbed over people, crossed the aisle and tried to restrain the man.

Passenger Syed Jafri said he saw a glow and smelled smoke. Then, he said, "a young man behind me jumped on him. Next thing you know, there was a lot of panic." Other eyewitnesses said that the hero passenger appeared to have suffered burns as he tried to stop the attack.

President Barack Obama immediately ordered heightened security and passengers flying to all US airports can expect tighter scrutiny over the coming days and weeks.

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 officers 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.

Transportation Security Administration officials said the agency was working "with our international partners on international measures for US-bound flights".

The threat level for US airline security has been high, or orange under the colour-coded system, since 2006, when a plot to detonate liquid explosives on trans-Atlantic airliners was disrupted.