Papua New Guinean police are yet to interview any suspects for the murder of Reza Barati in the offshore processing centre on Manus Island, more than five months after his death.

A PNG police spokesman, Dominic Kakas, said the investigation was currently under way and that it was an "ongoing case".

No suspects yet: Reza Berati. Credit:Kate Geraghty

Mr Kakas said no one had been charged, nor interviewed, for the murder of the 23-year-old asylum seeker. "It's got to be soon," he said.

On Monday, Immigration Minister Scott Morrison refused to comment on the progress of the Barati murder investigation, telling reporters in Canberra: "I have no further information to provide you on that than what is currently publicly available and as I have provided previously."