NSW officials blame their federal counterparts for signing up to an optional protocol of the convention against torture, suggesting the UN should focus its attention on countries that haven't accepted the international agreement.
Attorney-General Mark Dreyfus said no state or territory objected in 2017 when Australia ratified the protocol.
Representatives from the UN Subcommittee on Prevention of Torture undertaking a 12-day tour, said they were obstructed from carrying out their work, in violation of Australia's obligations.
Delegation head Aisha Shujune Muhammad said it was deeply regrettable, but the limited understanding of its mandate and a lack of co-operation from NSW and Queensland spurred a decision to cease the tour.
Mr Dreyfus said the federal government was disappointed in NSW for refusing access and regretted the UN's avoidable exit.
He said other unnamed jurisdictions had experienced problems, but had tried to resolve issues in good faith. The UN's departure would not change Australia's commitment, he added.
"It is vital that places of detention in Australia maintain the rights of those who are held within their walls," Mr Dreyfus said.
NSW Corrections Minister Geoff Lee told a budget estimates hearing on Monday he had confidence in the state's facilities.
"They meet and many times often exceed those of other countries," he said.
But the committee was told five older facilities, which housed hundreds of inmates, needed updating.
Corrective Services NSW commissioner Kevin Corcoran said the Inspector of Custodial Services had already delivered a report highlighting inadequate facilities.
"We've got our own standards … they don't meet those standards," he said.
Assistant commissioner Leon Taylor said some infrastructure dated back to the Victorian era and did not support "contemporary correctional practice".
Two facilities from the era had been closed and replaced with more modern facilities in the past 18 months and a new infrastructure strategy was being developed, he said.
Dr Lee said he would try and address the issue in his remaining months as minister.
"I will continue to advocate very strongly for our portfolio agency to receive money to upgrade and expand our facilities and retire the old facilities as soon as possible," he said.
Retiring MP David Elliott, who was NSW corrections minister when Australia ratified the protocol, said he told past premiers not to approve inspections.
"I'm not going to have UN inspectors from Iran and China and Cuba come into NSW jails and tell us that we're doing things wrong," he told 2GB radio on Monday.
None of those countries have ratified the protocol, nor has the United States, which has the world's highest per-capita incarceration rate.
Queensland Premier Annastacia Palaszczuk commented on her state's health department blocking access to inpatient facilities.
"My understanding was that they were facilitating those visits, but of course there are privacy issues that are involved, and we look forward to working with the UN to facilitate whatever access they need that is appropriate," she told reporters.
Mr Dreyfus said the UN inspectors were given access to Commonwealth-run detention facilities but did not specify which ones.
Academics and advocacy groups condemned the states for blocking access.
"Parties have an obligation to both receive the (subcommittee) in their territory and allow it to exercise its mandate in full, including by allowing unfettered access to places of detention," read a joint statement from Australian Lawyers for Human Rights and other groups.
41°C