By Jeremy Pelofsky

WASHINGTON (Reuters) - 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.

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 on a flight from Amsterdam to Detroit.

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

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.

In a sentencing memorandum filed in federal court in Detroit, prosecutors urged a judge to sentence Abdulmutallab to the maximum of life in a U.S. prison.

For the first time, prosecutors revealed new details of the plot, including Abdulmutallab's close connections to the al Qaeda leader, who has been linked to other plots against the United States.

Abdulmutallab went to Yemen in August 2009 and sought out Awlaki in mosques. He made contact, was taken to Awlaki's home in the desert and agreed to carry out an attack, according to the court papers.

He was then was sent to receive training from an al Qaeda bombmaker, Ibrahim Al Asiri, in an AQAP camp where they discussed the mission. Asiri delivered the underwear bomb to Abdulmutallab and trained him on how to detonate it.

Awlaki helped Abdulmutallab write a martyrdom statement and arranged for a "professional film crew" to film the five-minute message, prosecutors said in the sentencing memorandum.

"Although Awlaki gave defendant operational flexibility, Awlaki instructed defendant that the only requirements were that the attack be on a U.S. airliner, and that the attack take place over U.S. soil," the court papers said.

Prosecutors also asked permission to show at the sentencing hearing on Thursday a video the FBI created which simulated the bomb Abdulmutallab tried to detonate.

Awlaki, who was identified by U.S. intelligence as "chief of external operations" for al Qaeda's Yemen branch and a Web-savvy propagandist for the Islamist cause, was killed in an attack by missiles fired from multiple CIA drones in a remote Yemeni town, U.S. officials have said previously.

The U.S.-born cleric left for Yemen after the September 11, 2001 attacks. Also killed in the drone strike was Samir Khan, another American who turned to militancy and served as editor of "Inspire," a glossy magazine used as a propaganda and recruitment vehicle by al Qaeda in the Arabian Peninsula.

(Reporting By Jeremy Pelofsky; editing by Todd Eastham)