GENEVA (Reuters) - The United Nations called on Australia on Tuesday to take responsibility for around 800 refugees and asylum seekers stranded in a detention centre on Papua New Guinea where it said many lack medical and mental health care.

FILE PHOTO - Activists hold placards and chant slogans as they protest outside the offices of the Australian Immigration Department in Sydney, Australia, February 4, 2016. REUTERS/Jarni Blakkarly

The refugees - many from Afghanistan and Pakistan, along with Rohingya Muslims from Myanmar - were removed from a holding camp in the remote Papua New Guinea island of Manus in November when Australia decided to close it.

Australia’s government - whose policy of holding asylum-seekers in offshore camps has bipartisan political support - has said the centre that the group was moved to on the island was adequate and that the Papua New Guinea government was responsible for running it.

But Rico Salcedo, UNHCR regional protection officer, told journalists on Tuesday that Canberra had a duty under international law to take responsibility for the 800 who had been seeking sanctuary in Australia.

“What stood out the most from this mission ... was a pervasive and worsening sense of despair among refugees and asylum seekers,” he said by video link from Canberra after returning from a trip to Manus Island.

“Australia remains ultimately responsible as the state from whom refugees and asylum seekers have sought international protection for their welfare and long-term settlement outside of Papua New Guinea,” he added.

There was no immediate response from Canberra to the UNHCR comments on Tuesday.

Salcedo said that while services were still predominantly implemented by Australian-contracted providers, the Canberra government was no longer coordinating the operation there, leaving refugees and asylum seekers confused as to how they can obtain services.

At least 500 of the 800 remaining on Papua New Guinea (PNG)await solutions or resettlement in third countries, the U.N. High Commissioner for Refugees (UNHCR) says.

The UNHCR calls came as a group of 18 men departed PNG for U.S. resettlement. The men were part of a larger group that were approved for U.S. residency late last month.

Under the Obama administration, the United States agreed to take up to 1,250 refugees, but transfers have been slow under Trump.