The United Nations High Commissioner for Refugees says asylum seekers on Nauru and Manus face indefinite detention in unsafe and inhumane conditions.
The United Nations Refugee Agency has slammed Australia's treatment of asylum seekers as constituting arbitrary, mandatory and indefinite detention in unsafe and inhumane conditions.
UN High Commissioner for Refugees (UNHCR) officials inspected processing centres at Nauru and PNG's Manus Island in October, encountering harsh conditions they say failed to meet international standards.
Those conditions impacted profoundly on the men, women and children housed there, UNHCR regional representative Richard Towle says in a statement.
"In particular, they constitute mandatory detention that is not compatible with international law," he says in a statement.
"They do not provide a fair and efficient system for assessing refugee claims, do not provide safe and humane conditions of treatment in detention, and do not provide for adequate and timely solutions for recognised refugees."
Director of international protection Volker Turk said UNHCR understood Australia's determination to respond robustly to the challenges of people smuggling and dissuade people from dangerous sea voyages.
"Those responses must not neglect the compelling protection needs, safety and dignity of the individuals affected," he said in a statement.
UNHCR acknowledged some improvements, including better facilities and the start of processing on Manus.
It also noted efforts made to improve conditions on Nauru, which was hot, had little privacy for people in tents following riots, cramped conditions and mosquitoes.
Nauru was unsuitable for children who lacked access to adequate education and recreation facilities, UNHCR said.
"UNHCR is of the view that no child, whether an unaccompanied child or within a family group, should be transferred from Australia to Nauru," it said.
At Manus, the UNHCR officials observed what they termed a "pervasive" climate designed to encourage asylum seekers to choose to return home.
The report said UNHCR supported voluntary return for those fully informed and not in need of protection.
But it said it was concerned that some bone fide refugees might consider return because of the harsh conditions, long delays in processing and uncertainty about the final outcome.