UNHCR responds to Nauru water-board claims

The UN's refugee agency is concerned about what it says are "worrying issues" emerging from a Senate inquiry into abuse allegations at the Nauru immigration detention centre.

A security firm whistleblower told the inquiry asylum seekers were subjected to water-boarding.

UNHCR regional representative Thomas Albrecht told AAP it was difficult to verify whether such claims were an exaggeration or had real substance because of secrecy surrounding the centre's operation.