Senior Republican John McCain has insisted that the US will not reinstate waterboarding despite comments in favour of the practice from President-elect Donald Trump.
The Arizona senator pointed out that waterboarding and other harsh interrogation techniques are banned under US law and the Geneva conventions and warned that any attempt to bring them back would be challenged in courts "in a New York minute".
Waterboarding, or simulated drowning, was widely used on terrorist suspects during President George W Bush's administration in the aftermath of the 9/11 attacks.
The practice was banned by President Barack Obama on his second day in office.
"I don't give a damn what the president of the United States wants to do, or anybody else wants to do – we will not waterboard, we will not torture," McCain was quoted as saying at the Halifax International Security Forum by Business Insider.
"It doesn't work. If you inflict enough pain on somebody long enough, they're going to tell you whatever they think you want to hear to get it to stop."
Trump consistently spoke out in favour of waterboarding during his election campaign, saying that the US had to "fight fire with fire".
"I like it a lot. I don't think it's tough enough," the president-elect said in June.
But McCain, who was tortured as a prisoner of war during the Vietnam War, said: "My god what does it say about America if we're going to inflict torture on people?
"It makes it hard for us to make the argument about the moral superiority of our government and our way of life."
The senior Republican also spoke in favour of the North American Free Trade Agreement, which Trump has promised to scrap, and the yet-to-be-implemented Trans-Pacific Partnership.
"I think we are going to pay a terrible price for abandoning the TPP," McCain was reported as saying by Associated Press.
"You are going to see Chinese assertion of economic influence in the region, and possible dominance. All of these countries are now going to join with China in trade agreements and we're going to be out in the cold. Historians will judge us very harshly."