An Australian senator says his immigration minister told a "despicable" lie about the Good Friday attack on Manus Island in order to demonise asylum seekers.
Members of the Papua New Guinea defence force are alleged to have shot at the Manus Island facility more than 100 times.
PNG police and detainees said the attack was sparked by an altercation between drunken navy officers and detainees over the use of a football field.
Australian Immigration Minister Peter Dutton said it was a reaction to detainees leading a small boy into the centre.
Green Party senator Nick McKim went to Manus to investigate.
He said he had spoken with the local police commander and the local MP during the self-funded trip.
He met with detainees, he said, but was prohibited from entering the centre by the PNG immigration department due to the ongoing investigation into the attack.
"I've spoken to Inspector Yapu, who's the senior local police officer on the ground here, and he's standing by the comments he's made publicly that in fact that attack escalated out of a dispute over a football field," said Mr McKim from Manus.
"Peter Dutton's reason that he's given publicly, which I believe is a lie, is that it flared out of a young boy being led up into the centre," he said.
"Inspector Yapu has confirmed to me that that event did not lead to any complaint to the PNG police and he's not currently investigating and he regards it as a completely separate matter."
Mr Dutton was yet to respond to a request for comment, but had previously declined to reveal classified information to the ABC that he said supported his allegation.
Mr McKim implied the minister was attempting to vilify refugees by portraying them as paedophiles.
"What Peter Dutton was doing was dog-whistle politicking and once again trying to demonise detainees, demonise refugees and demonise people seeking asylum in the eyes of the Australian people," he said.
"It was a despicable thing for him to do ... He stands condemned for doing everything he can to engage in dog-whistle politics and demonising the men who Australia has incarcerated for so many years on Manus Island."
It was pointed out to the senator that the minister had since qualified his statement by explaining the incident with the small boy had led to an escalation in tension but perhaps not the attack itself.
Mr McKim said he would not be surprised if Mr Dutton was trying to "crab-walk" away from his statement, and that he also believed the minister might have blocked his entry to the detention centre.
"It wouldn't surprise me at all if Peter Dutton's fingerprints were on this one. It's supposed to be an open camp, the Australian government describe it as an open camp," said Mr McKim.
The senator was pleased, however, with the number of detainees who had come out of the centre to speak with him.
About 900 men, who entered Australia illegally by boat, have been detained at the centre for four years.
Most were fleeing conflict and persecution and have been found to be refugees.
About 200 have been denied refugee status although the determination process used on Manus has been described by lawyers as deeply flawed.
The indefinite detention of refugees on Manus and Nauru has been criticised as being meant to deter others from entering Australia by boat.
"There's been a consistent theme in what the detainees have told me that they are having their hope gradually extinguished," Mr McKim said.
"I've been inspired by the dignity and the bravery and strength of a lot of these people and I'm even more determined to be a stronger voice for them when I get back to Australia."