Home Affairs Minister Peter Dutton says Australians have been "conned" over controversial refugee medical transfer laws.
He has also shed more light on a refugee deal with the United States and defended the cost of reopening a detention centre on Christmas Island.
There have been 135 asylum seekers brought to Australia from offshore detention since the so-called medevac laws took effect in March.
Only 13 people have been hospitalised on the mainland, while five have refused treatment altogether.
"This was only ever about bringing people from Manus and Nauru - not for medical attention - but because that was the back door way to bring people to Australia," Mr Dutton told Sky News on Tuesday.
"If you're desperate enough to come to Australia for medical attention but you don't need to go to hospital, I think people can read between the lines."
More than 1100 asylum seekers have been brought to Australia for medical treatment in recent years - all but a handful of whom remain in the country.
None of those accepted under the medevac laws have been returned to offshore detention.
Despite the laws stating detainees are only in the country for a temporary purpose, Mr Dutton says he is powerless to stop them staying.
"Not only is it a con that people are coming here and not receiving medical attention, the most dangerous con, in my view, is that people can't go back," he said.
Six people transferred to Australia under the so-called medevac laws have been flagged as security concerns, with two more in the system.
"You have been forced to take people of bad character who, if they commit a crime while they're here, I can't deport them," Mr Dutton said.
"If they commit a serious crime of sexual assault or rape while they're here, I can't deport them back."
Mr Dutton said one person was alleged to have fought with the Iranian army, another was allegedly involved in a prostitution ring, while others were accused of being members of drug syndicates.
"They're here in Australia," he said.
The minister could not confirm whether the six people deemed of "bad character" had been placed in detention on the mainland.
Mr Dutton is now trying to unwind the medevac laws.
He will need support from Senate crossbencher Jacqui Lambie, who has not yet indicated which way she will vote when the repeal bill comes up next month.
Meanwhile, there have been 632 refugees sent to the United States from Papua New Guinea and Nauru.
Mr Dutton expects another 250 people will be accepted under the resettlement deal, which is about half of the 562 who remain in offshore processing.
The home affairs minister has also defended the $27 million it has cost to reopen the Christmas Island detention centre, despite only one family being held at the facility.
The centre was reopened in response to the medevac laws but they do not apply to the Tamil family currently in detention.
Mr Dutton insisted it had deterred people in PNG and Nauru considering "gaming" the medevac laws, as well as asylum seekers in other parts of the world, thinking about coming to Australia.