Sarah Hanson-Young has declared the culture of secrecy on Nauru "out of control" after she was barred from returning to the tiny country to investigate the plight of refugees.

The Greens senator has called on Malcolm Turnbull to intervene, insisting "Australians deserve to know what is being done in their name on Nauru".

She suspects the decision is payback for her role in exposing the extent of sexual and other abuse of detainees inside the Nauru detention centre more than two years ago.

The senator's allegations prompted the Moss review in October 2014, which found evidence of rape, sexual assault of minors and guards trading marijuana for sexual favours from female detainees.