US President Barack Obama has ordered a review of air security measures after a Nigerian man allegedly tried to blow up a trans-Atlantic jet on Christmas Day.Spokesman Robert Gibbs said the president wanted to know how a man carrying dangerous substance PETN had managed to board a flight in Amsterdam.
He said the system of watch-lists would also be examined after it emerged the man was listed and known to officials.
A US record for 23-year-old Umar Farouk Abdulmutallab was created last month.
Mr Gibbs told ABC News that the review would examine, firstly, the system of watch-lists used by government agencies, which includes three lists which become progressively shorter as risk increases.
'Dangerous substance'
The lists include a watch-list, with some 550,000 names on it, a "selectee" list with 18,000 people within the higher-risk category, and a "no-fly" list with 4,000 names of people who are not permitted to board planes.
Mr Abdulmutallab was placed on the lowest-risk list by US authorities in November 2009, after his father alerted authorities about the behaviour of his son.
Mr Gibbs said the number of people on the watch-list was "a huge number".
"The president has asked that a review be undertaken to ensure that any information gets to where it needs to go, to the people making the decisions. The president wants to review some of these procedures and see if they need to be updated," he said.
On 24 December Mr Abdulmutallab travelled from Nigeria to Amsterdam and then on to Detroit with an explosive device attached to his body, US officials say.
Shortly before the flight was due to land in the US, he allegedly attempted to detonate the device beneath a blanket but he was overpowered by passengers and crew.
Mr Abdulmutallab, the son of a prominent Nigerian banker, has been charged by US authorities with trying to blow up the Northwest Airlines flight as it was coming in to land.
US airlines especially have tightened security after the attempt, increasing screenings and body searches and, in some cases, confining passengers to their seats without pillows or blankets for the last hour of their flight.
Mitigation measures
Mr Gibbs said "air detection capabilities" would also be examined as part of the review.
"The president has asked the Department of Homeland Security to answer the - quite frankly - the very real question about how somebody with something as dangerous as PETN could have gotten onto a plane in Amsterdam."
PETN, or pentaerythritol, is the same material used by convicted shoe bomber Richard Reid who tried to destroy a trans-Atlantic flight in 2001.
Mr Abdulmutallab's route originally began in Yemen, from where he travelled to Ethiopia, then to Ghana and finally Nigeria.
According to Nigeria's information minister, Mr Abdulmutallab had arrived and flown out of Nigeria in the space of a single day.
"The man in question has been living outside the country for a while," said Dora Akunyili.
"He sneaked into Nigeria on the 24th of December and left the same day."
Nigerian authorities, who on Sunday pledged to co-operate fully with the US investigation, said screening would be enforced for all passengers passing through the country's 22 airports.
Wealthy or influential people and their families are often allowed to skip checks, media reports say.
Speaking to ABC News, Homeland Security Secretary Janet Napolitano said there was no immediate indication that Mr Abdulmutallab was part of a broader terror plot.
"Right now we have no indication that it is part of anything larger. But obviously the investigation continues. And we have instituted more screening and what we call mitigation measures at airports," she said.
