SYDNEY (AFP) - Papua New Guinea police Thursday said an investigation into a riot at an Australian detention centre on Manus Island that left an asylum-seeker dead "stinks of a major cover-up".r

Deputy Commissioner Simon Kauba said the findings of the probe, carried out on b

ehalf of the Australian government, "only hampers our on-going investigations into the riot" which also left 69 people injured in February.

"Our investigations have been frustrated from day one with a complete lack of cooperation from all involved including (detention centre security firm) G4S employees as well as the asylum-seekers themselves," Kauba said in a statement.

"In fact the asylum-seekers as well as G4S officials and other service providers refused to give their statements to us and made it known that they preferred to talk only to Australian lawyers." Under Australia's tough refugee policy, asylum-seekers arriving by boat are sent to detention centres on PNG's Manus Island or Nauru, a remote Pacific neighbour, for processing and permanent resettlement.

The 107-page review released Monday found Iranian asylum-seeker Reza Barati was "brutally beaten" to death by a Salvation Army worker.

It also found that PNG police had pushed over the fence and entered the compound before opening fire after G4S, which manages the centre's security, had left during the riot.

But Kauba said an initial investigation by local police found its officers did not enter the camp before or during the riot, were not involved in the violence and did not injure any asylum-seekers.

Police believe Barati's death was the result of injuries caused by four detention centre staff, two PNG locals and two foreigners, he added.

Kauba said PNG officers fired "warning shots into the air from outside the centre" that "helped to quieten the situation".

This contradicted the review's findings that police fired a number of shots into residential buildings in the centre and that some bullets hit walls about "chest height".

The police chief said his force's investigation into whether an asylum-seeker, who was shot in the buttocks, had been injured by one of his officers was being hampered by a lack of access to the detainees.

"The only way we can confirm this is if the injured man is brought forward and appropriate tests conducted to confirm the nature of the injuries sustained," Kauba said.

"Otherwise, this whole matter stinks of a major cover-up." Australian Immigration Minister Scott Morrison said Monday it was up to local police to lay charges over the disturbance and that the information used to prepare the report was handed over to PNG authorities.

According to latest immigration figures, Manus Island has 1,273 asylum-seekers, while a further 1,177 are being held on Nauru.