Australia has sent a boat full of asylum seekers to offshore detention in Nauru for the first time in nine years.
After the revelation at a Senate estimates hearing on Monday, the Labor government was accused of lacking transparency and failing to keep Australia's borders safe.
Home affairs department officials said on Monday 13 people remained on Nauru as of September after a boat carrying 11 people was intercepted the same month.
They declined to comment on "on-water matters" and would not say where the asylum seekers were intercepted, where they had come from, or if there were women and children among them.
The lack of detail prompted Greens senator Nick McKim to accuse the federal government of "outrageous secrecy".
Liberal senator James Paterson was also unimpressed, saying it was the ninth people-smuggling venture since Labor was elected last year.
"The most recent venture is a chilling reminder of the illegal arrivals we saw the last time Labor was in government," he said in a statement.
"The Coalition's (Operation Sovereign Borders) sent a clear message of deterrence to people smugglers looking to sell illegal voyages to Australia. This work is now being undone."
The detention centre in Nauru had been emptied of asylum seekers in June but the federal government kept the facility open.
The government rejected claims that high-risk offenders had entered Australia after being held on Nauru.
Independent Jacqui Lambie said she was told in a private briefing before the last election in May 2022 that up to 70 asylum seekers were deemed high risk.
Senator Lambie made a deal with former prime minister Scott Morrison to get asylum seekers off Nauru and Manus Island, unless they were a security risk.
The home affairs department's acting boss Stephanie Foster said no one with security concerns or terrorist links had been allowed into Australia for a temporary purpose, after Senator Lambie asked if any had links to Hamas.
Cabinet minister Murray Watt said it was important accusations had substantial evidence to back them up in a politically charged environment.
"If you're going to suggest that terrorist sympathisers are entering Australia that is a very big call to make at a time where the community is really worried, understandably, around the Middle East conflict and we're seeing a lot of tension within the community," he said.
Department assistant secretary Michael Thomas said people getting off the island were a mix of resettlers and those who had temporarily come to Australia.
People can be brought to Australia temporarily for medical treatment or before they are resettled in a third country.
When a person is brought to Australia from Nauru they are placed in detention as an unlawful non-citizen and remain there until the minister intervenes.
"A risk assessment process is undertaken at that point to make a determination about the best placement for them," Mr Thomas said.
A number of people had been resettled in third countries but it was hard to say whether they were the individuals being referred to "without knowing the exact number you're talking about," he said.
