US agents could use methods of torture on suspected terrorists once again because "it works", President Trump has said.

In comments which will prompt alarm among human rights groups and leading Republicans and Democrats, Mr Trump said he had spoken to "people at the highest level of intelligence" who told him torture "absolutely" works.

The new president said he would rely on the guidance of his CIA Director Mike Pompeo and Defence Secretary James Mattis as to whether he should allow the resurrection of techniques such as waterboarding during interrogations.

"When they [so-called Islamic State] are 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 told ABC's World News Tonight.

"I have spoken as recently as 24 hours ago with people at the highest level of intelligence and I asked them the question: does it work? Does torture work? And the answer was yes, absolutely.

"I will rely on Pompeo and Mattis and my group and if they don't want to do it that's fine. If they do, then I will work towards that end. I want to do everything within the balance you are allowed to do legally.

"But do I feel it works? Absolutely I feel it works."

The remarks came as it was reported Mr Trump is exploring the possibility of reopening so-called overseas "black site" prisons, where terror suspects were detained and tortured during President Bush's post 9/11 "War on Terror".

President Obama closed the secret prisons down following widespread condemnation and accusations of human rights violations.

Throughout his presidential campaign, Mr Trump condemned what he deemed to be a soft approach on terror by Mr Obama.

He strongly embraced the idea of torture and vowed to bring back "a hell of a lot worse than waterboarding".

A unused guard tower at Camp Delta in the US Naval base at Guantanamo Bay Credit: AP

John McCain, the former Republican presidential candidate who was captured and tortured during his Navy service in Vietnam, urged Mr Trump not to revive Bush-era torture techniques.

"The president can sign whatever executive orders he likes," McCain said in a statement.

"But the law is the law. We are not bringing back torture in the United States of America."

The Arizona Senator later told MSNBC that America's most respected military leaders - including Mr Trump's new Defence Secretary James Mattis - are opposed to torture, adding that he was "very confident that it wouldn't stand a day in court" if the Trump administration pushed for the use of it again.