US officials have begun taking fingerprints of asylum seekers in an Australian-run camp on the Pacific island of Nauru, signalling that vetting of applicants for resettlement in what US President Donald Trump called a "dumb deal" has restarted.

Australia agreed with former US president Barack Obama late last year for the United States to resettle up to 1,250 asylum seekers held in much criticised processing camps on Papua New Guinea and Nauru.

In return, Australia would resettle refugees from El Salvador, Guatemala and Honduras.

Mr Trump labelled the agreement a "dumb deal" on Twitter, but said he would stand by it.

Interviews with more than half a dozen detainees on Nauru confirmed the US Homeland Security officials arrived on Saturday, with meetings with detainees beginning today.

Two asylum seekers, who spoke on condition of anonymity because of fears of jeopardising their applications to settle in the United States, told Reuters by phone Homeland Security officials did not ask any specific questions.

"It was not a normal interview, they just collected fingerprints and took my height and weight," the Iranian refugee told Reuters.

Other refugees showed Reuters appointment slips to meet US officials.

Similar biometric data collection would begin at the Australian-run detention centre in Papua New Guinea in early April, detainees were told by immigration officials last week.

Australia maintains a strict policy of not allowing anyone who tries to reach the country by boat to settle there, instead detaining them in the camps on Nauru and PNG in conditions that have been harshly criticised by rights groups.

Some asylum seekers have spent years in the camps, with numerous reports of sexual abuse and self-harm among detainees, including children.

One 36-year-old woman told Reuters by phone from Nauru she did not want to be too hopeful about resettlement.

"For me, I really don't believe anything [about] when I get out from this hell," she said. "I heard too many lies like this in this three and half years."

A spokeswoman for Australian Immigration Minister Peter Dutton declined to comment. The Department of Homeland Security did not respond to a request for comment.

The US security interviews with asylum seekers on Nauru were cancelled last month amid uncertainty about what constituted "extreme vetting" Mr Trump promised to apply to the 1,250 refugees it agreed to accept.

Some asylum seekers said the latest developments gave them hope.

"I think the deal will happen, but the question we don't know is how many people will be taken by the US," Behrouz Boochani, an Iranian refugee held on PNG's Manus Island for nearly four years, told Reuters.

With mounting international pressure, officials at Manus Island centre are increasing pressure on asylum seekers to return to their home countries voluntarily, including offering large sums of money.