The Australian Federal Police refused a request from Papua New Guinea for an officer to help interview witnesses to the killing of asylum seeker Reza Barati on Manus Island.

PNG police said they needed the Australian help because some witnesses to the violence at the immigration detention centre in mid-February were reluctant to speak to local Manus Island investigators and had demanded instead to speak to Australians.

But the request last week for help was declined. ''The AFP does not have any plans to provide any further support to [the Royal Papua New Guinea Constabulary] regarding this matter,'' an AFP spokesman said.

''A request was made by the RPNGC to provide an AFP member as an independent person to an interview with a witness in this investigation. This request was declined due to the AFP having no operational jurisdiction in PNG, and suggested alternative options for the RPNGC to consider.''