The United Nations reaffirmed on Friday that torture is illegal and that refugees deserve protection, while ducking any direct criticism of remarks made by new US President Donald Trump.

Major human rights groups have denounced Trump's stance on torture and warned against restoring a CIA secret detention programme for interrogating terror suspects.

Trump is also reviewing spending, including at the UN, where the United States is the largest donor.

"International human rights law is clear on the absolute prohibition on torture," UN human rights spokesman Rupert Colville told a news briefing.

Pressed repeatedly to comment on Trump's remarks this week that torture "works", Colville noted that prominent US Senators including Republican John McCain, himself a torture victim, and Democrat Dianne Feinstein, who chaired an inquiry on the CIA programme under former President George W. Bush, had spoken out.

It was still very early days in terms of how the UN human rights office interacts with the new administration, he said. "We have to work out strategically what is going to be effective."

The UNHCR was also tepid in its comments on Trump's moves to restrict refugees. He is expected to sign an executive order that would include a temporary ban on all refugees, and a suspension of visas for citizens of Syria and six other Middle Eastern and African countries.

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"Of course UNHCR believes that refugees should be offered assistance, protection, opportunities for resettlement, regardless of their race, religion or ethnicity," UNHCR spokeswoman Vannina Maestracci said.

The US Department of Homeland Security has temporarily halted trips by staff to interview refugees abroad ahead of a likely shakeup of refugee policy by Trump, two sources said on Thursday.

During the election campaign, Trump decried former President Barack Obama's decision to increase the number of Syrian refugees admitted to the United States over fears that some fleeing the country's civil war might carry out attacks.

Some 25,000 refugees were resettled in the United States between October and year-end under UNHCR's program for the most vulnerable, Maestracci said.

A host of US federal government agencies are involved and extensive background checks are carried out, she said.

"I think it's fair to say that refugees coming into the United States to be resettled are some of the most vetted individuals entering the United States," Maestracci said.