NSW committed to letting UN human rights inspectors visit the state's jails before backflipping as the delegation was on its way to Australia, a federal budget estimates hearing has revealed.
A 12 day visit to Australia by a delegation from the United Nations Subcommittee on Prevention of Torture was cut short in October because of a lack of cooperation from NSW and Queensland.
The inspection, a condition of a human rights convention ratified by Australia in 2017, had been scheduled to take place during 2020 but was delayed over pandemic lockdowns.
Under its mandate, the subcommittee can carry out unannounced visits to all detention facilities and conduct private interviews with people deprived of their liberty.
Fielding a barrage of questions from Senator David Shoebridge, the secretary of the federal Attorney-General's department admitted NSW had previously committed to inspectors having unfettered access to state-run jails.
"We had not been advised prior to the visit that NSW would not admit entry to subcommittee inspections," Katherine Jones said on Monday.
"We were only notified on the day the subcommittee was arriving in Australia that NSW would not facilitate visits."
The visit was scheduled for October 16 to 27 before it was abruptly suspended.
Another senior official, Simon Newnham, confirmed all states and territories agreed to facilitate the visits to their facilities "including NSW".
Aisha Shujune Muhammad, the head of the four-member delegation, said NSW stonewalling the inspectors was "a clear breach by Australia of its obligations" under the convention.
"It is deeply regrettable ... the lack of co-operation stemming from internal disagreements, especially with respect to ... Queensland and NSW has compelled us to take this drastic measure," said Ms Muhammad in a statement.
"This is not a decision that the (subcommittee) has taken lightly".
At the time, Premier Dominic Perrottet defended his government's decision on the ground funding commitments sought from the federal government were not met.
He described the NSW prison system as "the strongest in the country".
"Our prison system is there ultimately to do one thing and that is: keep the people of NSW safe," he told state parliament.
"We've set up those oversights in our prison system and if people have issues ... you can raise them with the minister or the corrective services commissioner."
Attorney-General Mark Dreyfus slammed NSW's backflip in October as "disappointing".
The Optional Protocol to the Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment was ratified in 2017 by Malcolm Turnbull's government.