By Ehssan Veiszadeh of AAP
In a letter sent to Immigration Minister Chris Bowen, the United Nations High Commissioner for Refugees (UNHCR) Antonio Guterres said PNG had neither the "legal safeguards nor the competence" to process transferred asylum seekers on Manus Island.
Mr Guterres said PNG was not yet party to the UN conventions on torture and statelessness and warned the nation lacked the necessary legal framework to address refugee issues.
There was also a risk of local PNG authorities sending asylum seekers back to their countries of origin, particularly given the "porous and often unregulated" nature of its borders.
He concluded the country did not have the "legal safeguards nor the competence or capacity to shoulder alone the responsibility of protecting and processing asylum seekers transferred by Australia".
"At best, we would see the transfers as a shared and joint legal responsibility under the Refugee Convention and other applicable human rights instruments," Mr Guterres said in the letter dated October 9.
A spokesperson for the minister said the government was still on track to send the first group of asylum seekers to Manus Island within weeks.
"As part of the designation process we have consulted with and tabled correspondence by the UNHCR - and as always, we take on board issues they have raised," the spokesperson said.
"We continue to work with the PNG government on implementation and expect the first transfers ... occurring in coming weeks, with further details to be announced in due course."
They added that PNG had assured the Australian government it would assess asylum claims in-line with the Refugee Convention.
Australian Greens senator Sarah Hanson-Young accused Mr Bowen of ignoring expert advice about its offshore processing regime.
"The letter has revealed just how inadequate the situation on PNG is, where there isn't even one person with the relevant experience and training that is required to process refugees," she said in a statement.
"Desperate and vulnerable people are still doing whatever they can to seek asylum and that obviously won't change until we give them safer pathways."
The government ultimately hopes to be able to send up to 600 asylum seekers to Manus Island, which the Rudd government closed in 2008.
Meanwhile, another 40 male asylum seekers were transferred to Nauru's offshore processing facility on Friday.
The 17 Iraqis and 23 Sri Lankans will now be settled into their accommodation at the temporary facility.
This takes the total number of people transferred to Nauru to 254