The United Nations has unexpectedly terminated its anti-torture mission in Australia after inspectors were denied access by the Australian government to numerous prisons, with a major monitoring agency slamming the encounter as an "embarrassing debacle" on Monday.

The UN inspectors, who were tasked with examining facilities as part of a voluntary agreement to minimize inmate maltreatment, said they made the "dramatic" decision after being refused admission at "many" jails and detention centers.

Australia was in "clear breach" of its international commitments, according to lead inspector Aisha Mohammad, a Supreme Court judge in the Maldives. "Despite our numerous efforts to explain our preventative mandate, this was clearly not understood," she said.

Only three other countries have had anti-torture inspectors delay or postpone missions: Rwanda, Azerbaijan, and Ukraine.

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Australia adopted the Optional Protocol to the Convention Against Torture (OPCAT) in 2017, pledging measures that protect detainees and subject facilities to inspection.

Former prison inspector Steven Caruana coordinated the domestic body responsible for tracking Australia's implementation of the convention. "There can really be no excuse as to why the delegation was hindered," he told AFP on Monday. 

"Australia has had almost five years to prepare for this visit. Australia will now have to answer for this embarrassing debacle in front of the United Nations Committee against Torture." 

Rights abuse allegations 

Australia's unwillingness to accept the inspectors was due to a financing dispute between the federal and state governments. The federal government ratified the convention, but individual states and territories were responsible for putting it into action.

UN inspectors were blocked by New South Wales last week from a small courthouse jail, the UN delegation said. 

Queensland refused to let inspectors visit inpatient units at mental health facilities, according to the Queensland Health department.

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The UN delegation said it had "been prevented from visiting several places where people are detained... and was not given all the relevant information and documentation it had requested."

Human rights abuses have been reported repeatedly in Australia's jails, adolescent detention centers, and immigration compounds, particularly against Aboriginal people.

Australia has until January 2023 to meet its obligations. 

There are no penalties for missing the deadline, but Australia could be placed on a non-compliance list of countries with significant human rights concerns.