DETROIT - A federal judge on Friday entered a not guilty plea on behalf of Umar Farouk Abdulmutallab, the 23-year-old Nigerian accused of an attempt to blow up a Detroit-bound jetliner that has prompted a sweeping review of U.S. security procedures.

Abdulmutallab answered in a quiet, polite tones to a questions from U.S. Magistrate Mark Randon, who entered the not guilty plea on his behalf when Abdulmutallab's lawyer said her client would stand mute when asked for his plea.

He was arraigned on six charges, including attempted murder and the attempted use of a weapon of mass destruction to bring down a plane carrying 289 other people.

President Barack Obama in remarks on Thursday took ultimate responsibility for security failures that allowed Abdulmutallab to board the Detroit-bound airliner in Amsterdam, and Obama ordered reforms aimed at thwarting future attacks.

U.S. officials say Abdulmutallab tried to ignite explosives concealed in his clothing as the flight from Amsterdam prepared to land in Detroit, but was subdued by other passengers.

Linked to a Yemen-based branch of al Qaeda, Abdulmutallab has been held in a federal prison in Milan, Michigan.

The initial hearing took only a few minutes, and could set the stage for a trial that legal experts said is weighted heavily in the government's favor given the evidence, including Abdulmutallab's injuries.

Abdulmutallab, who walked into court unaided, could face life in prison.

It happened in an enclosed environment, in the air, with many witnesses, said Larry Dubin, a law professor at the University of Detroit Mercy.

Police closed off the snow-covered street approaching the federal building and limited the number of observers in court to fewer than 80 witnesses and reporters. Three bomb-sniffing dogs checked those arriving for the hearing.

A dozen people held up signs outside the courthouse, reading Islam is against terrorism and Not in the name of Islam.

Meanwhile, U.S. Attorney General Eric Holder said the use of full-body scans was a necessary invasion of privacy to ensure airplane passengers are safe and he predicted travelers would soon get as used to them as they have become to removing their shoes at airport security checkpoints.

We have to, in order to ensure our safety, give up certain amounts of privacy, Holder told a civic group in West Palm Beach, Florida, on Friday.

We have to use all the means we can to ensure that people can fly safely. The impact of if that had been successful in Detroit, the ripple effects of that on our economy, on our system of commerce, would have been huge, Holder said.

The federal case number is 2:09-mj-30526.

(Additional reporting by Bernie Woodall and David Bailey in Detroit and Jane Sutton in Miami; editing by Andrew Stern and Eric Walsh)