DETROIT - A mandatory life sentence for a Nigerian who tried to blow up a Detroit-bound plane is cruel and unfair, a defence attorney said Monday as he asked a judge to declare the punishment unconstitutional.

No one aboard Northwest Airlines Flight 187 except Umar Farouk Abdulmutallab was physically injured, Anthony Chambers said. Abdulmutallab's groin was severely burned when he tried to ignite a bomb in his underwear.

Abdulmutallab is returning to court for his sentence Thursday, four months after he pleaded guilty to trying to destroy an Amsterdam-to-Detroit flight on Christmas 2009. He said he was acting on behalf of al-Qaida. Two of the crimes carry a mandatory sentence of life in prison.

Abdulmutallab "fully accepted responsibility for his actions but the need for proportionality in terms of sentencing is paramount," Chambers said. "A mandatory life sentence under these circumstances is excessive."

Abdulmutallab, the well-educated son of a wealthy Nigerian banker, is representing himself, with Chambers assisting him as his standby counsel. Four or five passengers, just a slice of the nearly 300 people who were aboard Flight 187, are expected to speak at the court hearing this week.