The alleged terrorist behind the Christmas Day airliner plot is said to have told US agents there are more people "just like him" ready to carry out future attacks.
An al-Qa'ida group based in Yemen claimed responsibility yesterday for the failed attempt to bring down Northwest Airlines Flight 253 over Detroit as US president Barack Obama pledged to hunt down the plotters.
Meanwhile, photographs apparently showing the underpants filled with explosives worn by alleged bomber Umar Farouk Abdulmutallab were broadcast today by ABC News.
The American government pictures show the singed underwear with a six-inch packet of a high explosive called PETN sewn into the crotch, the US network reported.
ABC News said Abdulmutallab was carrying about 80g of PETN, more than one-and-a-half times the amount carried by "shoe bomber" Richard Reid in 2001 and enough to blow a hole in the side of an aircraft.
Abdulmutallab, 23, a former engineering student at University College London, has reportedly told FBI agents he is one of many would-be terrorists in Yemen ready to carry out attacks in the near future.
Al-Qa'ida in the Arabian Peninsula, an alliance of militants based in Saudi Arabia and Yemen, said the action was retaliation for a US operation against the group in Yemen.
The group said in an internet statement that the failed attack exposed the "large myth" of American and international security services and claimed only a "technical error" had prevented the bomb from detonating.
Mr Obama broke off his family holiday in Hawaii yesterday to announce he had launched reviews into airport security and the monitoring of suspected terrorists.
In his first public comments on the incident, he said: "A full investigation has been launched into this attempted act of terrorism and we will not rest until we have found all those responsible."
The US president added: "We will continue to use every element of our national power to disrupt, to dismantle and defeat the violent extremists who threaten us, whether they are from Afghanistan or Pakistan, Yemen or Somalia, or anywhere where they are plotting attacks against the US homeland."
Abdulmutallab tried to ignite his device as the flight from Amsterdam, carrying nearly 280 passengers, entered its final descent to Detroit on Christmas Day.
His former tutors at University College London, where he was a student between 2005 and 2008, described him as "well-mannered, quietly spoken, polite and able" and said he never gave any cause for concern.
He was president of the institution's Islamic society between 2006 and 2007, a spokesman confirmed.
Nigerian-born Abdulmutallab is being held at a federal prison in Michigan on a charge of trying to destroy an aircraft.
He apparently wrote of his loneliness and struggle between liberalism and Islamic extremism in a series of postings on Facebook and in Islamic chatrooms, the Washington Post reported today.
In January 2005, when he was attending boarding school, he wrote: "I have no one to speak too. No one to consult, no one to support me and I feel depressed and lonely. I do not know what to do. And then I think this loneliness leads me to other problems."
Home Secretary Alan Johnson said it was unlikely that Abdulmutallab acted alone and revealed that he was banned from entering Britain and placed on a "watch list" earlier this year.
Mr Johnson said the alleged terrorist was refused a new visa and was monitored since last May after applying for a bogus course.
Abdulmutallab's wealthy family said they believe he was radicalised while attending the British International School in Lome, the capital of Togo.
After he broke off contact, they approached foreign security agencies expressing concern about his state of mind and requesting "assistance to find and return him home".
British police and MI5 have been diverting resources to investigate the importance of the Nigerian's links to London.
Throughout the weekend, search teams combed the imposing mansion block in Mansfield Road, close to Oxford Street, where Abdulmutallab used to live in the capital.Reuse content