Washington - Al Qaeda leader Anwar al-Awlaki personally directed and approved the attempted bombing of a U.S. airliner which a Nigerian man tried to carry out on Christmas Day in 2009, according to new details released by federal prosecutors on Friday.

    Awlaki, who was a leader of the militant group's affiliate in Yemen, al Qaeda in the Arabian Peninsula (AQAP), before he was killed in a drone strike last year, directed Umar Farouk Abdulmutallab to conduct a strike aboard an American airliner over U.S. soil.

    "Awlaki's last instructions to him were to wait until the airplane was over the United States and then to take the plane down," according to court papers. Awlaki left it up to Abdulmutallab to pick the flight and date, the papers said.

    Awlaki also told him to avoid suspicion by not flying directly from Yemen to Europe. Instead, Abdulmutallab flew from Yemen to Ethiopia to Ghana and Nigeria before boarding a flight to Amsterdam and eventually Detroit.

    Abdulmutallab, 25, is due to be sentenced Thursday in Detroit and faces up to life in prison after pleading guilty to charges he tried to down a Northwest Airlines jumbo jet with 289 people aboard.

    The bomb, hidden in his underwear, failed to fully detonate and he was quickly subdued by passengers and crew. The incident led U.S. officials to quickly bolster airport security, deploying full-body scanners to try to detect hidden explosives.

    While hospitalized because of burns to his groin area from trying to ignite the explosives, Abdulmutallab told a nurse he had no history of trying to harm anyone. When she disputed that assertion by noting his bombing attempt, he replied: "That was martyrdom," according to the court papers.

    In October, Abdulmutallab pleaded guilty days after his trial began, saying he had wanted to avenge the killing of innocent Muslims by the United States. A lawyer for the Nigerian.