Donald Trump said he believed waterboarding "absolutely" works as he said the US should fight "fire with fire" in its efforts to tackle Islamic terrorists.

In a wide-ranging interview that covered how he felt receiving the nuclear codes to his controversial immigration policies, the US president said he would consult with James Mattis, his Defence Secretary, and Mike Pompeo, his CIA director, about what could be legally done to tackle radicalism.

"When Isis is doing things that nobody has ever heard of since Medieval times, would I feel strongly about waterboarding...?" he said in the ABC News interview, his first since taking office.

"I have spoken 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'.