The Obama administration admitted defeat in its efforts to prosecute the self-described mastermind of the Sept. 11, 2001, terrorist attacks before a civilian jury in New York City, announcing that Khalid Shaikh Mohammed and four others would be tried by a military commission at the U.S. naval base in Guantanamo Bay, Cuba.

The decision, announced Monday by Atty. Gen. Eric H. Holder Jr., marks a sharp political setback for President Obama, who had repeatedly pledged to use civilian courts to try "high-value" terrorism suspects. It also creates fresh uncertainty about the legal road ahead for senior Al Qaeda suspects now in custody.

A federal judge in Manhattan promptly dismissed a sealed grand jury indictment from December 2009 against Mohammed and the four others pending transfer of the case to the military tribunal. The existence of the 10-count, 81-page federal indictment against the five men was not previously known.

Several hours later, Navy Capt. John Murphy, chief prosecutor in the Pentagon's Office of Military Commissions, announced that charges would be filed "in the near future" to try the case at Guantanamo. Mohammed and his codefendants are among about 170 detainees at the military prison there.

"I intend to recommend the charges be sent to a military commission for a joint trial," Murphy said, adding that his office already was preparing its case.

In 2007, during a combatant status review tribunal hearing at Guantanamo, Mohammed confessed to the Sept. 11 conspiracy, as well as other lethal terrorist plots, and asked to be put to death. If military prosecutors seek the death penalty, he will not be allowed to plead guilty under the rules of military justice and will have to stand trial.

Mohammed's U.S. interrogators subjected him to waterboarding, a process that simulates drowning, 183 times in March 2003, shortly after he was captured in Pakistan, according to a report by the CIA. None of the statements given under such harsh interrogation procedures can be used against him, according to Obama administration policies.

By moving the trials to civilian court, Obama had hoped to demonstrate the fairness of the U.S. justice system. Civilian proceedings are more transparent and include civilian judges and jurors. In military tribunals, judge and jury are military officers.

But critics feared that a trial on U.S. soil would trigger terrorist reprisals and require an enormous outlay of funds for security. Many also worried that stricter standards for admissible evidence could result in more acquittals and lenient sentences.

Holder said at a news conference that he and the White House "reluctantly" reversed course because Congress passed legislation in December barring the use of federal funds to transfer detainees from Guantanamo to the U.S. In addition, he said, relatives of the nearly 3,000 people who were killed almost a decade ago in the attacks in New York, Pennsylvania and at the Pentagon were losing patience.

Holder said he was confident prosecutors would have prevailed in New York but took solace that the cases would proceed in the military system.

The New York indictment listed all of those who were killed, filling 36 pages.

"For the victims of these heinous attacks and their families, justice is long overdue, and it must not be delayed any longer," Holder said.

At the White House, Press Secretary Jay Carney suggested that the need to bring the five suspects to trial drove the decision to hand them to the military legal system. The administration has spent 15 months reviewing possible trial venues outside Guantanamo, including a vacant state prison in Thomson, Ill.

"The president's commitment here is this: Those who are suspected and accused of participating in those heinous attacks be brought to justice," Carney said. "That is his primary concern."

The decision, announced on the same day that Obama opened his reelection campaign, reflected a realization that the president cannot overcome political opposition to civilian prosecution of Guantanamo detainees and that he had to shelve his campaign promise to shutter the detention camp at the naval base.

On Capitol Hill, those who opposed a New York trial and sought to keep the Guantanamo prison open applauded the announcement.

Sen. Jeff Sessions (R-Ala.) said Obama's campaign promises were "built on the naive premise that softening America's image would somehow soften our enemies' resolve."

On the Democratic side, Sen. Charles E. Schumer of New York said the reversal was "the final nail in the coffin of a wrongheaded idea."