Umar Farouk Abdulmutallab was on a suicide mission when he attempted to detonate a bomb in his underpants as the plane, en route from Amsterdam, approached Detroit

The notorious underwear bomber's plot in 2009 to blow up a plane on Christmas Day failed because the explosives became 'degraded' after he wore the same pair of underpants for two weeks, according to a U.S. official.

Nigerian Umar Farouk Abdulmutallab was on a suicide mission when he attempted to detonate a bomb in his underpants as the plane, en route from Amsterdam, approached Detroit.

The bomb however failed to detonate aboard the flight, which was carrying nearly 300 people, but caused a brief fire that caused burns to his groin.

He was sentenced to life without parole in February 2012 after he pleaded guilty to all charges on the second day of his trial the previous October.

The head of the Transportation Security Administration said this week the bomb failed to detonate because of how long Abdulmutallab had been wearing his underwear.

John Pistole told the Aspen Security Forum: 'The bomber had had the device with him for over two weeks.'

Mr Pistole was then asked whether the bomb had become 'damp', to which he replied: 'Let's say it was degraded.'

During his trial, Abdulmutallab said the bomb in his underwear was a 'blessed weapon' to avenge poorly treated Muslims around the world.

After the bomb failed to detonate, passengers pounced on Abdulmutallab and forced him to the front of Northwest Airlines Flight 253 where he was held until the plane landed minutes later.

The head of the Transportation Security Administration said this week the bomb failed to detonate because of how long Abdulmutallab had been wearing his underwear

In 2009, months before the attack, he travelled to Yemen to see Anwar al-Awlaki, an American-born cleric and one of the best-known al Qaeda figures, according to the government.

He told investigators that his mission was approved after a three-day visit with his mentor.