A prominent Papua New Guinean politician says he will go to court to stop Australia from sending asylum seekers to his country.

The PNG government is still considering Australia's proposal to establish a processing centre for asylum seekers on Manus Island in the country's far north.

The governor of the National Capital District, Powes Parkop, told Lateline the proposal is unconstitutional.

"The law in Papua New Guinea is very clear, that we cannot keep people in detention without charging them," he said.

Before entering politics, Mr Parkop was a human rights lawyer, and he says he will challenge the proposal in court if it goes ahead.

He says Australia is taking advantage of the poor economic conditions on Manus Island by offering development assistance to get an agreement.

Mr Parkop's objection comes after ABC's Lateline obtained an internal paper from the Canberra office of the United Nations Refugee Agency (UNHCR) which shows the unease within the organisation over any agreement to reopen the Manus Island facility.

Unlike Malaysia, which has formed an in-principle refugee swap deal with Australia, Papua New Guinea is a signatory to the UN Refugee convention.

But the UNHCR paper raises serious concerns about Papua New Guinea's ability to handle asylum seekers.

"Overall assessment of PNG's compliance under the 1951 Convention: Very poor," the paper reads.

It goes on to say Papua New Guinea has no legal framework to address refugee issues, has porous borders and little protection for refugees.

The UN has released a statement criticising the ABC for releasing the internal documents, and saying the internal documents did not represent its official view.