Australia exposed an Iranian asylum seeker to torture and ill-treatment during his years in detention, a UN committee has found, amounting to a breach of international obligations.

On Wednesday evening, the UN committee against torture released its decision on the case of an asylum seeker who arrived on Christmas Island by boat in 2013 after fleeing Iran in fear of persecution.

He was transferred by authorities to Manus Island in Papua New Guinea where he remained for about three years, in “harsh conditions and subjected to serious violence”, the committee found, including having his throat slit by a security guard.

In 2019, he was evacuated to Australia for medical treatment but remained in immigration detention for a further three years despite “serious physical and mental health conditions” the committee found, before being released into the community on a bridging visa in 2022.

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In its refutation of the complaint, Australia argued it did not exercise effective control over detention facilities in Papua New Guinea and said the complainant received appropriate medical and mental health care.

It further argued that his detention in Australia was lawful and subject to review, and that he was no longer detained at the time the committee considered the case.

The committee rejected the arguments, contending Australia’s funding, management and contracting of services at Manus were sufficient to establish jurisdiction under the convention, in line with the UN human rights committee’s decisions on another two cases regarding Australia’s processing centre on the island of Nauru.

Last week, a UN watchdog ruled that Australia violated the rights of asylum seekers arbitrarily detained on Nauru, in a warning to other countries intent on outsourcing asylum processing.

Jorge Contesse, a committee member said human rights protection and international law obligations “do not disappear when detention facilities are relocated offshore”.

“Geography is not the test, but whether a state has placed a person in a situation where it has the power to prevent harm and fails to do so,” he said.

“Where a state creates and maintains a system of offshore detention and retains decisive influence over the conditions, it remains responsible under international law.”

The committee found Australia failed to take effective measures to prevent torture and ill-treatment during the complainant’s detention in Papua New Guinea, or to provide adequate rehabilitation and medical care, amounting to “torture and cruel, inhuman or degrading treatment, in violation of articles 2(1) and 16 of the convention”.

The committee also determined the complainant’s subsequent immigration detention in Australia and prolonged deprivation of freedom were not based on individualised assessment and also amounted to cruel, inhuman or degrading treatment.

It found that Australia failed to demonstrate that the detention was reasonable, necessary, or proportionate, particularly in light of the complainant’s prior years of offshore detention and documented vulnerability, including acute medical needs.

It further recalled its “longstanding concerns about Australia’s offshore processing policy”, which it said had “repeatedly exposed asylum seekers to prolonged detention, uncertainty, and conditions causing severe physical and mental suffering”.

The committee called on Australia to provide the complainant with full redress, including compensation and rehabilitation, to afford him an opportunity to have his protection claims examined by relevant authorities and to provide a guarantee that similar violations of the convention against torture would not occur in the future.

A spokesperson for the federal government said it was Australia’s “consistent position” that people in regional processing countries “do not engage our international obligations”.

“We are carefully considering the views of the UN Committee against Torture in this individual complaint,” they said.

“We engage in good faith with these processes and the government will provide its response in due course.”