Immigration Minister Scott Morrison says new information casts doubt on initial reports that a Manus Island detainee died from injuries he sustained outside the island’s detention centre during riots there.

Mr Morrison says he is unsure where 23-old Iranian asylum seeker Reza Berati suffered his fatal injury on Monday night and who was responsible.

In a statement, Mr Morrison says he has information indicating the majority of the unrest, and attempts to restore order, took place within the perimeter of the centre.

Australia and Papua New Guinea are both conducting investigations into the violence.

The Greens and asylum seeker advocates have said that Mr Berati was “murdered” on the island.

Greens immigration spokeswoman, Senator Sarah Hanson-Young, says eyewitness accounts since Monday have been dismissed and that the government is in cover-up mode.

“An appalling abuse of power by this Minister and the government to try and cover up the facts,” she said.

“The Australian people are shocked at what happened on Manus Island.

“There is a firm view in the community that things have gone too far, Manus Island should be shut down and we should be treating people with more dignity and respect.”

The Government says it will wait for the findings from its official review before commenting on individual reports about what took place.

Review of Manus riot may take months

Mr Morrison warned on Friday that an investigation to be conducted by former Attorney-General’s Department secretary Robert Cornall would take “some time” to gather the facts about the “very serious incident” in which 67 asylum seekers were injured.

The review is likely to take months, but the Mr Morrison says it could take longer.

“I have indicated over the next few months I would like to see this matter at least get to some point of knowledge on this,” he told reporters in Canberra.

“If that is not possible, it will take longer and [Mr Cornall] will be given support to do that.”

Mr Berati arrived at Christmas Island with no family members on July 24 and was transferred to PNG one month later under the resettlement policy introduced by former prime minister Kevin Rudd.

One asylum seeker was flown to Australia for treatment for head injuries as a result of this week’s riots. Four others, including one shot in the left buttock, are being treated in Port Moresby, while another asylum seeker is awaiting transfer to the capital.

Mr Morrison says he takes responsibility for things that happen on his watch.

“I do take responsibility for things that happen within my portfolio under my management, of course I do,” he said.

“Since we came into office, I have been taking steps every day to try and upgrade and get the offshore processing facilities in a far better shape.”