President George W Bush signed a law today authorising tough interrogation and prosecution of terrorism suspects.
Mr Bush, trying to help Republicans maintain control of the US Congress by emphasising national security, called the Military Commissions Act of 2006 "one of the most important pieces of legislation in the war on terror."
American Civil Liberties Union
Human rights groups charge that the measure would allow harsh techniques bordering on torture, such as sleep deprivation and induced hypothermia.
In a White House East Room ceremony, Mr Bush praised members of Congress who approved the law over the opposition of the Democratic leadership in both the Senate and House of Representatives.
"Every member of the Congress who voted for this bill has helped our nation rise to the task that history has given us. Some voted to support this bill even when a majority of their party voted the other way," Mr Bush said.
Much of the new law, which critics say still does not protect detainees' rights and predict will face legal challenge, was negotiated in September after senior Republicans rebelled against Mr Bush's plan.
The new law means Mr Bush can continue a secret CIA program for interrogating terrorism suspects whom he believes have vital information that could thwart a plot against America.
Mr Bush said the law will allow intelligence professionals to question suspects without fear of being sued by them later.
"This bill spells out specific recognisable offenses that would be considered crimes in the handling of detainees so that our men and women who question captured terrorists can perform their duties to the fullest extent of the law," he said.
The White House has refused to describe what techniques will be allowed or banned.
Critics and legal experts have predicted the new law will draw vigorous court challenges and could be struck down for violating rights guaranteed under the US Constitution.
They cited provisions that strip foreign suspects of the right to challenge their detentions in US courts and what they described as unfair rules for military trials.
Mr Bush insisted the law complies with the spirit and letter of international agreements.
"As I've said before, the United States does not torture. It's against our laws and it's against our values," he said.
The law also establishes military tribunals for terrorism suspects, most of whom are held at the US military prison at Guantanamo Bay, Cuba.
The law was prompted by a Supreme Court ruling in June that said Mr Bush lacked legislative authority in setting up his first system of military commissions.
Future legal battles will likely also end up in the high court. Shortly after Mr Bush signed the law, the Republican National Committee issued a press releasing headlined, "Democrats would let terrorists free" and listed the names of many House and Senate Democrats who opposed it.
The American Civil Liberties Union expressed outrage, calling the new law "one of the worst civil liberties measures ever enacted in American history."
"Nothing separates America more from our enemies than our commitment to fairness and the rule of law, but the bill signed today is an historic break because it turns Guantanamo Bay and other US facilities into legal no-man's-lands," said ACLU Executive Director Anthony Romero.