SYDNEY (Reuters) – An outbreak of dengue fever at an Australian refugee detention centre in the tiny Pacific island nation of Nauru sparked calls on Thursday for greater oversight at the facility, which has been criticised by rights groups and the United Nations.

Australian Immigration Minister Scott Morrison’s office said that medical officers at the centre had confirmed three cases of the potentially fatal tropical disease, which is transmitted by mosquitoes.

Two of those affected by the sickness are potential refugees awaiting processing, while the other was a member of staff working at the centre, they said.

“All three people have been isolated and are receiving appropriate treatment and are expected to make a full recovery,” a spokeswoman for Morrison said in a statement.

But Senator Sarah Hanson-Young, immigration spokeswoman from the opposition Greens Party, said that outbreaks are inevitable in crowded camps like the one on Nauru and called for greater independent oversight of the overseas refugee detention system.

“The government can’t control these types of outbreaks in the harsh detention camp environment. With seven families to a tent, it’s impossible to keep children safe from the disease,”

she said in a statement.

Australia uses detention centres in Nauru and on Manus Island in Papua New Guinea to process would-be refugees sent there after trying to get to Australia, often in unsafe boats after paying people smugglers in Indonesia.

Canberra’s tough stance on asylum seekers, including offshore processing and a blanket ban on people arriving by boat ever settling in Australia, has been criticised by the United Nations and other groups as illegal and inhumane.

The U.N. High Commissioner for Refugees in a November report said neither centre had a “fair and efficient system for assessing refugee claims” nor provided “safe and humane conditions of treatment in detention”.

Nauru in particular has come under fire after President Baron Waqa earlier this year unilaterally sacked the nation’s entire judiciary, one aspect of what critics have called a creeping authoritarianism there.

Critics say that Australia has been unusually silent about developments in Nauru in order to ensure that the camp, which is vital to its immigration policy, stays open.

In February, a riot at the detention centre on Manus Island in Papua New Guinea left at least one asylum seeker dead and 77 more injured.