A United Nations report Monday criticised Australia's immigration camp on Papua New Guinea, warning living conditions are harsh and asylum-seekers' detention arbitrary.
The UN High Commissioner for Refugees called for no more children to be sent to the camp on remote Manus Island, which was established as part of Australia's plan to ship refugees offshore to deter more from coming.
In its report, the UNHCR warned of "very significant inadequacies in the legal and operational framework governing the transfer, treatment and processing" of asylum-seekers.
Detaining asylum-seekers on a mandatory and indefinite basis, without possibility for review, amounted to "arbitrary detention which is inconsistent with international human rights law", it added.
"The key failing is that there are in place no legal frameworks for the processing of refugee claims," UNHCR regional representative Richard Towle told the Australian Broadcasting Corporation.
"If the sole purpose of transfer from Australia to Papua New Guinea was to process people, one would expect there'd be some kind of process in place for people when they get there."
The UNHCR said the delays and uncertainty for asylum-seekers about whether they will eventually be classed as refugees had left many feeling distressed and confused.
"They are in closed detention, without a process in sight. They feel they have been forgotten," Towle said.
A UNHCR team that visited Manus for three days last month said both Australia and PNG were committed to adequate procedures and conditions being in place despite the difficulties faced in remote Pacific locations.
But it said at the time of their visit, living conditions for most of the 221 detainees on Manus were harsh and, for some, inadequate.
"The hot and humid weather made the temporary accommodation very uncomfortable," Towle said.
Australia began dispatching asylum-seekers to Manus Island in November as part of a new policy of sending boatpeople offshore to deter others from making the risky journey to Australia which has claimed hundreds of lives.
Canberra's other offshore camp, on the small Pacific nation of Nauru, has also been criticised by rights advocates, with Amnesty describing conditions there as "appalling" and likely in breach of obligations to refugees.
Australia last year dealt with a record 17,202 asylum-seekers arriving by boat. The majority pay people-smugglers for passage from Indonesia on leaky wooden vessels, and sinkings are routine.