A Nigerian reported to have links to al-Qaeda is being questioned after an attempted act of terrorism on a plane arriving in the US, officials say.They say the 23-year-old man was trying to ignite some kind of explosive device as the airliner approached Detroit.The flight from Europe landed safely after the man was overpowered by passengers and crew.Witnesses said he burnt his leg but no-one else was hurt among the 278 passengers and 11 crew on board.Officials have described the device as a mixture of powder and liquid which failed to go off properly.One terrorism expert said it looked as though a new way of concealing explosives on the body was involved.President Barack Obama, on holiday in Hawaii, has ordered increased security for air travel.The suspect's name was in a database indicating "a significant terrorist connection" although it did not appear on a "no-fly" list, said Mr King.Mr Mutallab reportedly told investigators he had links to al-Qaeda and had received the explosives in Yemen.According to some US and Dutch media reports, he is a student at University College London.Mr King also said investigators were looking into whether the incident was part of a larger plot and a "worldwide alert" had been raised.The Department of Homeland Security said "additional screening measures" had been put into effect since the incident.'Lot of panic'Northwest Airlines Flight 253 had begun its descent towards Detroit Metropolitan Airport on Friday afternoon when the incident occurred.The Airbus 330, which had originated in Amsterdam, was about 20 minutes from landing when passengers noticed something was wrong.One of them, Syed Jafri, said he had been seated three rows behind the suspect and had seen a glow and smelt smoke.Then, he said, "a young man behind me jumped on him"."Next thing you know, there was a lot of panic," Mr Jafri added.As the suspect was being tackled, he was reportedly shouting and a passenger said she had heard the word "Afghanistan".Another unnamed passenger heard a "little pop", then saw "a bit of a smoke and then some flames".After "yelling and screaming", the passenger added, "they took him out and it was really quick".Fellow passenger Melinda Dennis said the man had been severely burned on one leg, and a fire extinguisher and water were used to put out the fire.The suspect later told the US authorities he had had explosive powder taped to his leg and used a syringe of chemicals to mix with the powder that was to cause explosion, the ABC television network reports.Dr Sally Leivesley, an adviser on terrorism and public protection, told the BBC: "This has looked as though it's a first attempt of a new way to use the body to conceal explosives.""They may be concealing the explosives on the human body - but on the inside upper leg, and we only know this by seeing a very badly burnt leg on the suspected perpetrator."Source: BBCWhite House spokesman Bill Burton said the president was monitoring the situation.'Terrorist connection'The Nigerian, named as Abdul Mudallad, had third-degree burns, said Peter King, a Congressman on the US House of Representatives Homeland Security Committee.