By Anne Davies
THE search for any accomplices of the Nigerian man charged with attempting to blow up a Northwest Airlines flight on Christmas Day has gathered new urgency after al-Qaeda claimed responsibility and authorities were told there might be more bombers trained to attack US flights.
Al-Qaeda in the Arabian Peninsula - a terrorist cell based in Yemen and led by a former personal secretary to Osama bin Laden - issued a statement saying it had trained and equipped Umar Farouk Abdulmutallab.
An FBI photo of Abdulmutallab's underwear and the alleged explosives
The group said the bombing attempt was in response to US-backed air strikes on the group in Yemen this month.
The New York Times said Abdulmutallab told FBI agents he was connected to the al-Qaeda affiliate, which operates mostly in Yemen and Saudi Arabia, through a radical Yemeni cleric whom he contacted online.
"It would be naive to believe that he was the only one out there," said Peter Bergen, a senior fellow at the New America Foundation and CNN's security analyst.
The explosive substance Abdulmutallab was said to be carrying - pentaerythritol tetranitrate, or PETN - was not used by terrorist groups other than al-Qaeda, Mr Bergen said. Shoe bomber Richard Reid also used PETN in his attempt to blow up a US flight in December 2001.
Several US television networks have aired FBI photos of Abdulmutallab's underwear - cut from his body by the flight crew - which show a white powder, said to be PETN, sewn into the singed fabric.
Experts say the substance is stable even if knocked or bumped, but just 100 grams when detonated can blow a hole in the skin of an aircraft. Abdulmutallab was sitting in seat 19A, above the wing fuel tanks.
In a further twist, a Michigan lawyer, Kurt Haskell, has said he saw Abdulmutallab in the company of a well-dressed Indian man at the Northwest Airlines gate in Amsterdam.
The Indian man explained that his friend was Sudanese and did not have a passport. Later Mr Haskell recognised the man without the passport as the suspect. It is not clear whether Abdulmutallab travelled without a passport.
This use of PETN is similar to that in an August attack on Prince Mohammed bin Nayef, Saudi Arabia's deputy interior minister. The prince's attacker, Abdullah Hassan al-Asiri, was killed when he detonated the bomb in his underwear. The prince received minor injuries.