In its latest damning report
, rights group Amnesty International accused the Australian government of turning the tiny island into an "open-air prison."
"The government of Australia has isolated vulnerable women, men and children in a remote place which they cannot leave, with the specific intention that these people should suffer," said Anna Neistat, Amnesty's senior director for research.
Prime Minister Malcolm Turnbull told the Australian Broadcasting Corporation Tuesday the claims were "absolutely false."
"The Australian government's commitment is compassionate and it's strong," he said.
Successive Australian governments have defended the policy of detaining refugees offshore as humanitarian, to deter people smugglers from making the treacherous journey and to stop people drowning at sea.
Repeated claims, denials
According to Amnesty, more than 1,100 asylum seekers and refugees are currently held on Nauru, a tiny island of just 10,000 people some 3,000 kilometers (1,864 miles) off the coast of Australia.
The latest Australian government figures put the total number of detainees at 410, including 49 children.
The center was set up to process asylum claims, but the Australian government has made it clear that even confirmed refugees will never be settled on the mainland.
For the report, Amnesty interviewed more than 100 people in Nauru and Australia, who recounted instances of sexual assault, neglect, poor healthcare and even torture at the detention center.
One detainee told researchers his life on Nauru was like "dying a thousand times."
"In Iraq, you get just one bullet or a bomb, and it's over, and here I'm slowly dying from the pain," he said.
'Racist, false' reporting
The Nauru government operates the detention center with support from Australia and private contractors. It was re-opened in 2012 after a surge in asylum seekers arriving in Australia arriving by boat.
It's not the first time the countries have had to defend the center.
Earlier this month, the UN's Committee on the Rights of the Child said found many cases of "attempted suicide, self-immolation, acts of self-harm and depression"
among children who had lived in prolonged "detention-like conditions."
And on Monday night, a report on the Australian Broadcasting Corporation's "Four Corners" program about the conditions on Nauru elicited a stinging rebuke
from the Nauru government.
"From start to finish (the report) was denigrating, racist, false and pure political activism," it said in a statement.
In a statement Monday, UNICEF Australia said "the reported decline in children's mental health, well-being and their development status is very disturbing."
The charity urged Canberra to "find a permanent solution for children and families on Nauru."
In January 2016, CNN spoke to former and current child detainees at the Nauru camp, who said it was "the worst place (they'd) ever seen for children
Australia's immigration department said in a statement Monday that it "takes the health and safety of refugees and transferees in Nauru very seriously and welcomes independent scrutiny of Australia's support of regional processing arrangements."
According to UNICEF
, the Nauru government charges Australia a monthly fee of $2,270 (3,000 AUD) per refugee and $756 (1,000 AUD) per asylum seeker every month.
Amnesty estimates that total costs of deterrence policies "such as turnbacks, offshore processing, and mandatory immigration detention" was upwards of $7.3 billion (9.6 billion AUD).
Despite this, and widespread criticism of ongoing human rights abuses on the island, support for the camps remains strong in Canberra.
Last month, Prime Minister Malcolm Turnbull defended
the country's record on immigration in a speech to the United Nations General Assembly.
During the general election earlier this year, opposition leader Bill Shorten pledged a "more humane and safer approach to asylum seekers," but his Labor party remains committed to offshore detention.