Operation Sovereign Borders commander Angus Campbell is being sent to Manus Island to assess security measures at the detention centre following a deadly riot this week.
Lieutenant General Campbell arrives on Thursday morning and will report back to Immigration Minister Scott Morrison with any suggested security improvements.
Iran, Labor and the Australian Greens want answers over the death of a 24-year-old Iranian asylum seeker during a fracas outside an Australian-run detention centre on Manus Island.
The man, an ethnic Faili Kurd, was among the first asylum seekers sent to PNG under former Labor prime minister Kevin Rudd's resettlement deal with the PNG government in July 2013, the Refugee Action Coalition says.
The man died after the Monday night riot, in which 76 other asylum seekers were also injured, with five requiring medical evacuations.
Australian ambassador to Iran Paul Foley on Tuesday spoke to Iran's foreign ministry about the death. Consular director Seyyed Hossein Mirfakhar was reported to have expressed Iran's "protest and discontent" about the "practice of violence and mistreatment" that led to the death.
The Department of Foreign Affairs and Trade said only that "Ambassador Foley met officials from the Iranian Ministry of Foreign Affairs to discuss the death of an Iranian national".
Opposition foreign affairs spokeswoman Tanya Plibersek said it was a "bit rich" of Iran to criticise Australia's treatment of asylum seekers considering its own human rights record.
PNG authorities are investigating the death.
After Labor's immigration spokesman, Richard Marles, demanded an independent inquiry into the violence, Mr Morrison confirmed someone from outside his department will investigate the incident.
"We need to understand why the Manus Island detention facility is melting down under Morrison's watch," Mr Marles told reporters in Canberra.
However, he said the PNG detention centre was the linchpin of Australia's strategy of stopping asylum-seeker boats, and there was no need to stop transferring asylum seekers there.
Mr Morrison said the inquiry would be conducted along the same lines as those under the previous Labor government into fires and riots at Nauru detention centre, Villawood and Christmas Island.
Mr Morrison said the mood was calm and quiet at the detention centre overnight, but 51 security staff are enroute to Manus Island from Brisbane to help beef up protection at the facility.
Manus Island local MP Ron Knight said the actions of PNG police in the riots would be scrutinised.
"The mobile squad of Papua New Guinea is rated as the second-toughest police force in the world and they don't play around," he told ABC Radio.
"If it's found the police acted in the wrong circumstances, police will be charged."
Mr Morrison confirmed the mobile squad were present on Monday night.
"They were never to my knowledge in the camp," he said.
Refugee Action Coalition spokesman Ian Rintoul said the Iranian man's death was a murder, not a tragic incident as Mr Morrison had described it.
He accused Mr Morrison of being selective in describing the injuries of asylum seekers. He said Mr Morrison did not reveal that one Iranian asylum seeker airlifted to Port Moresby had his throat slit during the riots.