"The use of torture to extract evidence from detainees held at the US military jail in Guantanamo Bay has tarnished the image of the US legal system and alienated allies in the war on terror, a human rights group says.
"The use of evidence tainted by torture and other inhuman treatment is pervasive and systematic in the cases of prisoners held at Guantanamo Bay, and has already infected legal judgments made there," Human Rights First said in a report titled 'Tortured Justice'.
By hearing testimony extracted under torture when trying Guantanamo detainees, the United States is "tainting the legitimacy of the proceedings, both at home and in the eyes of the international community; alienating US allies and empowering terrorists", it said.
'Tortured Justice' was released two days after US President George W Bush vetoed legislation on intelligence funding because it called for interrogation methods to be limited to techniques outlined in a US military manual.
That would have excluded waterboarding, a method of controlled drowning, widely seen as a form of torture.
In vetoing the bill on Saturday (local time), Mr Bush called hardcore interrogation methods "one of the most valuable tools in the war on terror", and praised them for preventing another attack on the United States, such as those on September 11, 2001."