An Iranian asylum seeker detained on Nauru has made a report about his alleged mistreatment by Nauruan police to the United Nations human rights agency.

The man claims he was detained for more than 30 hours in a bare police cell that was wet with the urine of his guards.

The man has told the ABC and staff from the Office of the High Commissioner for Human Rights that he was arrested and detained without charge after trying to see his sister.

• Senate inquiry slams Nauru detention centre
• Senator spied on at Nauru: whistleblower
• Australia stays silent on Nauru

She had just tried for the second time to kill herself after being allegedly raped on the island in May.

The woman has since been transferred to Brisbane in a serious condition while her brother and mother have remained on Nauru.

On the night he was arrested, the 20-year-old man was waiting with his mother for her medication when he heard his sister’s scream.

He knows now she had drunk insecticide.

“I just run, because I heard the screaming sound, because I understood that something happened to my sister,” he said.

The incident was witnessed by a fellow detainee, named Fariborz, who said the guards were very rough.

“Australian officers came and they grabbed his hands. They grabbed him in such a way as if they had arrested a criminal from Daesh group,” he said.

“His shoulder blades were being bent, because they had pulled his arms behind him.”

Fariborz said Nauruan police arrived soon afterwards.

“His only offence was that he wanted to see his sister for just five seconds. And he kept begging them,” he said.

“No matter how much he begged them, they still did not let him see his sister, and they took him to prison.”

-ABC