Nauru has been accused by a United Nations official of breaching its international obligations by failing to set up an independent body to investigate torture and human rights abuses in the Australian-run detention centre on the island.
The Nauru government has also refused access to several United Nations groups wanting to inspect the centre.
Fairfax Media reports that Nauru is in breach of a February deadline to establish an independent local body to regularly inspect the detention centre, a commitment it was supposed to meet after ratifying a UN anti-torture convention last year.
The chairman of the UN's sub-committee on prevention of torture, Malcolm Evans, says all member states are required to establish such a body for overseeing detention centres.
Earlier this month, investigators from the working group on arbitrary detention said they were blocked from entering Nauru after an earlier invitation had been sent, but the Nauru government says it had never asked the group to visit the island.