A UN human rights expert voiced alarm on Friday that US President Donald Trump might allow torture in interrogations, and called for senior officials from George W Bush's administration to be prosecuted for allowing the illegal practice.

US officials responsible for the secret detention, rendition and torture programmes run by the Central Intelligence Agency (CIA) included "those in the most senior positions" under Bush, said Ben Emmerson, UN special rapporteur on protecting human rights while countering terrorism.

"To hear President Trump, in the first days after his inauguration, glibly extolling the virtues of torture as a weapon in the fight against terrorism, and confirming his personal willingness to authorise the use of torture if asked to do so, was enough to make my blood run cold," Mr Emmerson said.

Mr Trump has acknowledged that US Defense Secretary Jim Mattis disagrees with him about the usefulness of torture in interrogation and said he would defer to him on the issue.

There was no immediate response from the US delegation to the 47-member state forum in Geneva.

Mr Emmerson, a British barrister and international criminal justice expert, said that Mr Trump's comments showed a "staggering level of ill-preparedness to govern." He was making his final speech to the UN Human Rights Council after six years in the independent post.

A veteran CIA clandestine service officer who ran one of the agency's "black site" prisons set up after the 9/11 attacks has been named deputy director of the US spy agency.

Mr Trump's nominee to be the director of national intelligence, former Republican Senator Dan Coats, has raised concerns over his record on the previous US use of so-called enhanced interrogation techniques, such as waterboarding, which are widely seen as torture.

"If one of the most powerful nations in the world, a permanent member of the Security Council, is once again prepared to abandon our collective values on the pretext of defending them, then one is left to wonder whether anything at all has been achieved in the last 15 years," Emmerson said.