An Iranian refugee held on Manus Island for more than three years before escaping Papua New Guinea to seek asylum in Fiji has been forcibly returned to Port Moresby.
Loghman Sawari, 21, was reportedly nabbed by Fijian police on the way to submit his claim for asylum on Friday morning before being taken to Nadi airport and bundled onto a plane bound for PNG.
The UNHCR says it is "gravely concerned" for Mr Sawari's welfare after his return, which proceeded despite the agency's interventions.
"The UN refugee agency had sought assurances from the government of Fiji this week that he would have access to Fiji's national asylum procedures," the UNHCR said in a statement.
"All asylum-seekers are entitled to have their claims for refugee status considered fairly and in accordance with the 1951 Refugee Convention, to which Fiji is signatory."
The UNHCR has long called for refugees and asylum-seekers in PNG to be moved to humane conditions outside the country, the statement said.
Amnesty International claims Mr Sawari, an Ahwazi Arab, has endured violence, intimidation, harassment and homelessness on the streets of Lae in PNG.
"We know he's in a vulnerable mental state and the incident this morning - being arrested and taken to the airport and separated from his lawyer - would have been quite traumatic in any circumstances," Kate Schuetze from Amnesty International told AAP.
"I'm very concerned right now that the authorities will try to arrest, detain or question him, which would be the worst possible thing for his health and wellbeing."
His case is extreme and he must not be left to languish on Manus Island, Amnesty says.
The Australian government pushed the young man into a desperate position and must now take responsibility for Mr Sawari and bring him to safety, the group says.
Australian immigration officials would not be drawn on whether they'd been involved in the matter or would be once Mr Sawari was back in PNG.
"The settlement of refugees in PNG is a matter for the PNG government," a department spokesman said.
"The reception and processing of refugee claims in Fiji is a matter for the Fijian government."
Fijian and PNG officials have been contacted for comment.
