Doctors Without Borders says it is deeply concerned for the health and well-being of its patients in Nauru.
The humanitarian organisation was ordered to leave the island at the weekend and told its free services are no longer required.
Doctors Without Borders has confirmed that its mental health care services in Nauru have been terminated.
It describes the mental health situation of asylum seekers and refugees there as "beyond desperate".
It's been operating on the island since late last year treating the mental health needs of both Nauruans and refugees.
It said all of its international staff have now left the island.
The international charity had identified cases of schizophrenia and family violence among the asylum seekers and high rates of depression especially among children.
About 900 refugees are detained in Nauru indefinitely at the behest of Australia - including about 100 children.
The Nibok refugee settlement, Nauru. Photo: Pool / NZ Herald / Jason Oxenham
