Papua New Guinea’s immigration department has moved dozens of asylum seekers to a Port Moresby prison complex.

The men, who have all been deemed non-refugees, were being moved on Monday to the Bomana Immigration Centre, a detention facility annexed to the Bomana prison.

A letter from the PNG immigration and citizenship authority (ICA) informed the men of the transfer and ordered them to surrender their mobile phone, any medication, and to pack up their personal property.

“You will not leave room. Your meals and drinks will be provided to you in your room. If you are on medication we will administer this to you,” it said.

The Bomana Immigration Centre was formally announced in 2014, and was funded by Australia at a reported cost of about $20m.

In June, after a young man attempted to take his own life, and damaged accommodation in the process, refugees and asylum seekers in the Hillside Haus accommodation centre in Lorengau were given the choice of moving to another Manus Island facility or transferring to Port Moresby. Many moved to Port Moresby, spread across three hotels.

Some were sent to Port Moresby’s Citi Boutique and Hodava hotel. Despite not being in detention, residents have been subjected to arbitrary rules and restrictions, including those held in Citi Boutique only allowed out for two hours every second day.

Those awaiting medical treatment have for many years been accommodated at the Granville Motel.

Behrouz Boochani, a Kurdish Iranian journalist and refugee on Manus Island, said more than 50 men had been marked for transfer to Bomana. He accused the PNG government of targeting men for “punishment” and of seeking to prevent their transfer to Australia under the medevac system – for which several had been approved.

A separate announcement from the ICA said the intent to move non-refugees to Bomana had been publicised “for many years”, while they continued to encourage non-refugees to depart voluntarily.

It said those who are currently held in Granville Motel – largely for the purpose of getting medical care in Port Moresby – would not be sent to Bomana “at this time”.

However anyone who was absent from the hotel overnight would be detained and transferred. Anyone else who failed to comply with rules would be deemed “unsuitable for the flexible accommodation arrangements” and detained until they left PNG.

While some non-refugees had left voluntarily and others had been sent home, an estimated 100 or so men remain in PNG, unable to be deported because their country of citizenship refuses to accept involuntary returns.

Ian Rintoul, spokesman for the Refugee Action Coalition in Australia, accused PNG of adopting Australia’s policy of indefinite detention “by stealth”.

He said the 2016 PNG supreme court determination that the Manus Island detention centre was unlawful applied equally to Bomana, and predicted it would be challenged in court.

“It is now very clear that the excuse of Hillside repairs was a ruse by immigration to shift the asylum seekers into Bomana. There was never any intention of returning them back to Manus Island,” he said.

“Many of those being detained are deemed not to be refugees although they have never had a refugee determination in PNG … The so-called ‘negatives’ should be released. There should have been a review of all their cases and any refugee determinations a long time ago.”

Last month the ICA detained three “unlawful non-citizens who were failed asylum seekers”.

PNG Chief Migration Officer, Solomon Kantha, said the men were detained after “all other efforts to encourage compliance have failed”, and that they had “abused” the privileges of the flexible accommodation arrangements in Port Moresby.

“It is a matter of public record that ICA encourages voluntary departure of all persons without a right to remain in PNG and for failed asylum seekers, we provide considerable financial assistance to support their return.”