The company responsible for security at the Manus Island detention centre has hit out at allegations staff acted inappropriately.
"Our personnel on duty during the disturbances acted with courage, strength and determination to protect those in our care," security company G4S said in a statement on Wednesday night.
An Iranian man was killed and almost 80 others were injured when violence erupted at the centre on Monday.
Papua New Guinean police attended the centre and fired shots. There have been mixed reports about how the trouble began and whether it stemmed from inside the compound.
"We take these allegations seriously and we as a company do not tolerate violent or abusive behaviour from our staff," the G4S statement said.
Guards on duty at the Manus Island centre don't carry weapons, it added.
PNG police are investigating the violence, and the Australian government has offered assistance.
Justice Minister Michael Keenan, who is visiting Port Moresby, said he had received assurances from his PNG counterpart, Kerenga Kua, and Police Minister Nixon Duban that the investigation would be thorough.
"Following these discussions, I remain very confident that the PNG authorities are best to investigate the circumstances surrounding what is a very regrettable incident," Mr Keenan said.
G4S said it would co-operate fully with the investigation.
