Photographs taken by detainees at Australia's centre for asylum seekers on Papua New Guinea's Manus Island are said to confirm the camp's poor conditions.
The Refugee Action Coalition says after detainees sent the photos to relatives, the Australian immigration department blocked their access to phone and internet.
A spokesperson, Ian Rintoul, says the blockage for four days last week is a determined act of reprisal by Australia's immigration department to keep the conditions on Manus Island secret.
He says the detainees' photos of their accommodation are quite different to the department's publicity shots.
"We call them dongers, they're often used for temporary accommodation for the housing and mining and things like that but they're very thin tin walls, no doors, no windows, all the things that we've been told about the heat, the lack of air conditioning, the lack of ventilation, the need for people to actually sleep outside to get away from the heat - they were the first glimpses we had of real life on Manus Island."
Ian Rintoul says one of the big issues about the island is that historically it has been a haven for malaria and dengue fever.
The Australian government has declined to comment on the matter.