Military trials arranged by the Bush administration for detainees at Guantanamo Bay are illegal, the United States Supreme Court ruled Thursday.

The court found that the trials — known as military commissions — for people detained on suspicion of terrorist activity abroad do not conform to any act of Congress. 

U.S. soldier keeps guard at the military-run prison at the Guantanamo Bay U.S. Naval Base, Cuba. The Supreme Court said U.S. President Bush was wrong to create military tribunals for the detainees at Guantanamo.
Brennan Linsley/Associated Press

The justices also rejected the government's argument that the Geneva Conventions regarding prisoners of war do not apply to those held at Guantanamo Bay.

Writing for the 5-3 majority, Justice Stephen Breyer said the White House had overstepped its powers under the U.S. Constitution. "Congress has not issued the executive a blank cheque," Breyer wrote.

President George W. Bush said he takes the ruling very seriously and would find a way to both respect the court's findings and protect the American people.

Salim Ahmed Hamdan, before his arrest in Afghanistan and detention at Guantanamo Bay. He admits to being Osama Bin Laden's driver but denies any military involvement against the United States.
Neal Katyal/Associated Press

"I haven't had a chance to fully consider this but we will work with Congress to find a way forward,"  Bush said during a news conference in Washington with visiting Japanese Prime Minister Junichiro Koizumi.

The Supreme Court case was brought by lawyers representing one of 10 detainees scheduled for trial. Salim Ahmed Hamdan has acknowledged having been Osama bin Laden's driver and bodyguard, but denies taking part in attacks against the United States. Hamdan is charged with a single count of conspiring to harm U.S. citizens. 

Ruling reverses decision

The ruling reverses a decision by a lower court that said the trials could go ahead. Military commissions were last used by the U.S. to try Japanese suspects after the Second World War.

The Bush administration had argued that neither military courts martial nor U.S. civilian courts were appropriate for trying the Guantanamo detainees because much of the evidence would involve sensitive issues of national security.  

The commissions comprised five senior military officers, and most sessions were scheduled to be held in private. A limited amount of media coverage was allowed. Defendants were represented by both military and civilian lawyers. 

Hamdan's military lawyer, Lt.-Cmdr. Charles Swift, hailed the ruling as "a return to our fundamental American values and a high-water mark in legal history."

Human-rights groups have said the military commissions were overly secretive and little better than kangaroo courts.

Canadian affected

Among the 10 affected by the ruling is 19-year-old Omar Khadr, a Canadian who is scheduled to face a military commission in the fall. One of his lawyers, Nathan Whitling, says the Supreme Court ruling should prompt Canada to ask for his client's extradition to stand trial in Canada.

"The Canadian government has been sitting on the sidelines for far too long," Whitling told CBC news Thursday, "Khadr's detention is now clearly ruled to be illegal and he must to returned to Canada for trial."

Speaking in recent weeks, Bush has said he would like to close down the Guantanamo Bay detention facility, sending some detainees for trial in their home countries and releasing those found innocent.

Many U.S. allies, including Britain, have called for the prison to be closed. However, speaking before the decision was handed down, the prison's commander said he doubted that would happen. 

"The impact [of a court decision against the tribunals] would be negligible," Rear Admiral Harry Harris told Reuters.

There are an estimated 450 foreign detainees being held at the Guantanamo Bay facility.