Lawyers are investigating taking Australia to the International Criminal Court over its offshore detention centres, Amnesty International says.
The human rights advocacy group has issued a report that says Australia's treatment of all its 410 detainees on Nauru - 55 of which are children - amounts to torture.
Amnesty's senior crisis director Anna Neistat interviewed dozens of people on the island.
She said Australia had put them there with the specific intention that they should suffer.
"The system is illegal and we show in our report in great detail how Australia is violating its multiple international obligations, including an obligation not to torture," she said.
"There are lawyers who are communicating with the International Criminal Court - it's not Amnesty International yet, but we are in touch with them as well, who believe there is enough evidence for the ... court to investigate Australia's offshore processing."
Dr Neistat said one man told her that his pregnant wife had tried to kill herself, and she met children who had tried to kill themselves multiple times.
She said New Zealand should take a lead in exerting international pressure on Australia.
New Zealand offered in 2013 to take 150 of the detainees on Nauru, but Australia said it must deal direct with Nauru. The New Zealand government has said it won't consider a separate settlement with the island.
Dr Neistat said New Zealand had a crucial role as one of Australia's key partners.
"International pressure should start from the region where New Zealand is undoubtedly the most serious player, who could challenge Australia's policy, and to a certain extent show to Australia that things can be done differently."
Australia's Department of Immigration secretary Mike Pezzullo denied the allegations Australia was breaching international conventions.
"I refute categorically both on behalf of my own department and by way of displaying government policy in this regard that it's not the Australian government's position, nor the position of this deptartment, that we flout any laws international or otherwise."