Christians in the U.S. are looking to new CIA Director Mike Pompeo to tread the high moral on torture after new President Donald Trump claimed waterboarding "works."

President Trump controversially suggested in comments to ABC News that torture could be justified when dealing with suspected Islamic State militants because "we're not playing on an even playing field."

"When they're chopping off the heads of our people and other people. When they're chopping off the heads of people because they happen to be a Christian in the Middle East, when ISIS is doing things that nobody has ever heard of since medieval times, would I feel strongly about waterboarding? As far as I'm concerned, we have to fight fire with fire," he said.

On waterboarding specifically, Trump said he would "rely on" Pompeo and defence secretary James Mattis to decide on which methods to use, and that he would be supportive if waterboarding were to be reintroduced.

The comments have alarmed the Reverend Ron Stief, executive director of the National Religious Campaign Against Torture, who said in an op-ed in The Christian Post that Pompeo should stand by the anti-torture stance of his confirmation hearings.

"Director Pompeo has affirmed that he understands that torture is illegal," he said. "We hope that he holds to that position as CIA Director and we pray that he also understands that torture is immoral. Jesus himself was a victim of state-sponsored torture – and it is something that all Christians, and indeed all people, have a duty to oppose."

Christians are not the only ones to have expressed serious concern over President Trump's comments.

Kate Allen, of Amnesty International, wrote in British newspaper The Metro that Trump is wrong to suggest waterboarding is effective.

"Torture doesn't 'work' in terms of obtaining useful information – terrified people in great pain will say whatever it is they think their tormentors want to hear," she said.

"Torture doesn't work in terms of delivering justice – information extracted under torture is rightly inadmissible in a court. And torture doesn't work in the way that Mr Trump seems to think it will work."

Moreover, she said Trump was mistaken in his belief that torture could help to 'keep America safe.'

"More likely the opposite," she wrote. "Would-be terrorists will feel emboldened by signs that major countries like the USA are resorting to torture. It shows the extremists they're starting to have an impact."