Four refugees transferred from the Nauru detention centre have arrived in Cambodia and have been taken away in a van with curtains covering the windows.

Two Iranian men, an Iranian woman and a Rohingya man from Myanmar arrived in Phnom Penh on a commercial flight.

The International Organisation for Migration (IOM) then took them to their villa at a secret location.

The refugees did not speak to the media, with Australian immigration officials saying the four did not want to jeopardise the safety of their families.

In a statement, the IOM said the group were being taken to temporary accommodation in the Cambodian capital to undergo language training as well as "cultural and social orientation".

"They're here, they're healthy and we ask for privacy for them," IOM regional spokesman Joe Lowry said.

The four are the first refugees to be transferred from Nauru as part of Australia's offshore processing policy.

As part of the deal Australia is giving the Cambodian government $40 million in aid and giving the IOM $15.5 million to support all refugees transferred there for a year.

"Cambodia clearly has no will or capacity to integrate refugees permanently into Cambodian society," Phil Robertson from Human Rights Watch said following the transfer.

"These four refugees are essentially human guinea pigs in an Australian experiment that ignores the fact that Cambodia has not integrated other refugees and has already sent Montagnards and Uighur asylum seekers back into harm's way in Vietnam and China."

In a statement, Amnesty International Australia said Cambodia's track record of protecting asylum-seekers was "poor" and called on Canberra to "cease the transfer of asylum seekers and refugees to third countries where they are not adequately protected from human rights abuses".

A spokesman for Immigration Minister Peter Dutton said he would not be commenting on the transfer.

ABC/wires