The federal government says asylum seekers on Manus Island and Nauru rejected for resettlement by the United States could use the medevac bill to come to Australia.

The government has confirmed the US refused to take 265 people from offshore detention after completing its own security checks.

Home Affairs Minister Peter Dutton told Sky News on Tuesday that under the medevac bill, passed last week against the government's wishes, they may be able to come to Australia.

"Under Labor's plan most certainly and that's a concern.

"I think now they're starting to understand the ramifications of what it is they've imposed on our border protection system."

Mr Dutton did not confirm whether the US automatically rejected all Iranians and Somalis in line with Donald Trump's travel bans.

The medevac bill, passed with the support of the crossbench, gives doctors more say in medical transfers of asylum seekers in offshore detention.

The bill still allows the Home Affairs minister to reject transfers on the basis of national security or bad character.

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ASIO checks could take months

Doubts have also been raised about Australia's chief intelligence organisation's ability to conduct its own assessments of sick asylum seekers recommended for medical treatment within the 72-hour timeframe set out in the legislation.

ASIO boss Duncan Lewis told a Senate estimates hearing on Monday it may take months to conduct proper checks in some cases.

AAP

"There will obviously be limitations on how fast we can respond," he said.

"If the person has a different kind of background, where they have come from some place and the records may not be complete, it can take months and months and months."

Nauru bans remote medical assessments

In another blow to the medevac bill, the Nauruan government has passed legislation limiting medical evacuations based on overseas assessments by doctors.

Prime Minister Scott Morrison said he was unsure what the impact of the new Nauruan laws would be.

"It's not quite clear what they've done and how that will play out," Mr Morrison told 3AW on Tuesday.

"What's happened in Nauru is a good example of what happens and how Labor didn't think through what playing around with border protection laws will do."

Report on 'ASIO leak' criticised

Mr Lewis also used his Senate estimates appearance to slam The Australian newspaper's reporting of an "ASIO leak" about the medevac bill.

"The advice that ASIO gave was not what was represented on the front page of The Australian newspaper."

The Australian's front page report 'Phelps bill a security risk: ASIO', published on February 7, that ASIO advice suggested almost all of the remaining 1000 people on Manus Island and Nauru could come to Australia under the medevac bill.

However, Mr Lewis said his organisation's advice was limited to matters related to the application of the ASIO Act.

In the lead up to the vote on the legislation, the government repeatedly claimed that security agencies had warned that the bill would weaken Australia's borders and restart the people smugglers trade.