Amnesty International says authorities have failed to adequately investigate complaints of violent crimes committed against asylum seekers held at Australia's expense on the Pacific atoll nation of Nauru.

The London-based human rights group found in an investigation of Nauru released on Monday that it appeared that no Nauruan had been held to account despite allegations of dozens of sexual assaults and physical attacks from 1,159 asylum seekers and refugees who live among 10,000 locals on the tiny island.

Australia attempts to deter asylum seekers from Africa, the Middle East and Asia from trying to reach Australian shores by boats from Indonesian ports by sending them to immigration camps at Nauru or Papua New Guinea. Genuine refugees among them are told they will never be resettled in Australia.