An Iranian refugee who attempted to seek asylum in Fiji could face criminal charges after being forcibly deported back to Papua New Guinea.
PNG's immigration and foreign minister, Rimbink Pato, has also vowed to tighten border security after Loghman Sawari was deported from Fiji for travelling to Nadi on a false passport.
"We will receive him and take the necessary steps to ensure he is properly questioned and, if appropriate, brought before the courts, noting he is a refugee who has had mental health issues," Mr Pato said.
"Tendering false statements or documents as part of any application for a passport or travel document is a criminal offence in PNG. Breaches will be investigated and those breaking the law will be prosecuted."
The United Nations refugee agency has expressed grave concerns about the welfare of Mr Sawari, who was 17 when he was transferred to Manus Island after attempting to come to Australia by boat.
A spokesperson for UNHCR's Regional Representation in Canberra, Catherine Stubberfield said that the agency was "profoundly concerned for his well-being," stressing that "after almost four years spent in harsh and isolating conditions on Manus Island, Mr. Sawari's sense of helplessness and hopelessness is acute."
"UNHCR urges the Government of Papua New Guinea to ensure that he is treated in accordance with human rights law and standards," she said. "The need to extend much-needed care to this extremely vulnerable young man is critical."
Trauma worker Janet Galbraith has also appealed for Mr Sawari to be offered sanctuary in another country, saying: "Having spoken with Loghman many times since he arrived in Fiji, I believe that this is the end for him. He is unable to survive any longer in this brutal and abusive system. His emotional and mental health have been fragile for a long time and none more so than now."
Friends and supporters of Mr Sawari have not heard from him since he was taken from a plane at Port Moresby airport on Friday for questioning.
The director of Fiji's Human Rights and Anti-Discrimination Commission, Ashwin Raj, said the deportation was in clear breach of international law and had "the possibility of exposing him to inhuman and degrading treatment".
"The deportation of Mr. Sawari raises fundamental questions about Fiji's capacity to balance the imperatives of national security with its international human rights obligations," Mr Raj said.
Mr Sawari flew to Fiji under a false name last week, telling Fairfax Media it was his final attempt to be free. "If I go back (to PNG) they will make me crazy or they put me in the jail. I'm sure about that," he said.
He was 17 when he was transferred to Manus Island in August 2013.