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WASHINGTON (CNN) -- The U.S. Supreme Court on Thursday strongly limited the power of the Bush administration to conduct military tribunals for suspected terrorists imprisoned at the U.S. Navy base in Guantanamo Bay, Cuba.

The 5-3 ruling means officials will have to come up with a new policy to prosecute at least 10 so-called "enemy combatants" awaiting trial. It does not address the government's right to detain suspects.

The case was a major test of President Bush's authority as commander in chief during war. Bush has aggressively asserted the power of the government to capture, detain and prosecute suspected terrorists in the wake of the attacks of September 11, 2001. (Watch analyst say administration has to start over -- 3:50)

At the center of the dispute was a Yemeni man, Salim Ahmed Hamdan, captured in Afghanistan in 2001 shortly after the 9/11 attacks. Officials said he has admitted being a personal assistant, bodyguard and driver to al Qaeda leader Osama bin Laden.

"The military commission at issue is not expressly authorized by any congressional act," said Justice John Paul Stevens, writing for the majority.

The tribunals, he said, "must be understood to incorporate at least the barest of those trial protections that have been recognized by customary international law."

"In undertaking to try Hamdan and subject him to criminal punishment, the executive [Bush] is bound to comply with the rule of law that prevails in this jurisdiction," Stevens wrote.

"Congress has not issued the executive a 'blank check,' " Justice Stephen Breyer wrote in a concurring opinion. "Indeed, Congress has denied the president the legislative authority to create military commissions of the kind at issue here."

Breyer noted, however, that "nothing prevents the president from returning to Congress to seek the authority he believes necessary."

The other justices in the majority were Ruth Bader Ginsburg, David Souter and Anthony Kennedy.

"To the extent there is latitude to work with the Congress to determine whether or not the military tribunals will be an avenue in which to give people their day in court, we will do so," Bush said at a news conference with Japanese Prime Minister Junichiro Koizumi. (More reaction)

The ruling means the Bush administration will have to adopt a military commission system for trying accused terrorists that meets international standards.

The court's ruling also establishes that federal courts have jurisdiction to hear appeals involving "enemy combatants" held overseas in U.S. military custody. The Bush administration had argued they lacked it.

Late last year, Congress passed and Bush signed the Detainee Treatment Act, which ostensibly limited court intervention over the prisoner issue.

Senate Majority Leader Bill Frist said Thursday afternoon he would introduce legislation after the Fourth of July break that would authorize military tribunals.

"To keep America safe in the war on terror, I believe we should try terrorists only before military commissions, not in our civilian courts," said the Tennessee Republican.

Dissenting in the ruling were justices Antonin Scalia, Clarence Thomas and Samuel Alito, each of whom entered separate opinions.

Scalia called the court's reasoning a "mess," and Thomas wrote that the ruling would "sorely hamper the president's ability to confront and defeat a new and deadly enemy."

"The president's decision to try Hamdan before a military commission for his involvement with al Qaeda is entitled to a heavy measure of deference," Thomas said.

"It seems clear that the commissions at issue here meet the standard" established by the government to try the accused terrorists, Alito wrote.

Chief Justice John Roberts did not vote, recusing himself because he ruled on the case at the appellate level.

Hamdan's lawyers argued that Bush exceeded his authority by setting up military commissions to try terrorist suspects, whom the administration terms "enemy combatants," rather than prisoners of war. (Watch military lawyer defend terror suspect -- 2:18)

They also argued that the government's charge of conspiracy against Hamdan is not allowed under international standards of law for prisoners of war, and that earlier federal courts had rejected that standard as well, since it was too broadly defined.

The administration's position was that the term means detainees do not have the rights usually afforded prisoners of war, as outlined in the Geneva Conventions.

The enemy combatant designation, according to the Bush administration, means the suspect can be held without charges in a military prison without the protections of the U.S. criminal justice system, such as the right to counsel -- a status the court rejected.

The Guantanamo Bay facility opened in 2002 and holds about 460 men suspected of links to al Qaeda and the Taliban.

Many world leaders have pressured Bush to close the camp, and he said last week he was considering doing so, noting he would decide after the court ruled.

"I'd like to end Gitmo, like it to be over with," he said at a European Union summit in Vienna.

"One of the things we will do is that we will send people back to their home countries. We have about 400 people left; 200 have been sent back. There are some who need to be tried in U.S. courts," Bush said.

"They are cold-blooded killers. They will murder somebody if they are let out on the street. And yet we believe there ought to be a way forward in the court of law."

Most of the prisoners were captured in Afghanistan, where U.S. troops are still battling remnants of the Taliban, the Islamic movement that harbored al Qaeda when it ruled Afghanistan from 1996 to 2001.