An asylum seeker at the Manus Island detention centre has alleged he and another detainee were tortured, physically assaulted, threatened with rape and forced to sign papers withdrawing their witness accounts about the night Iranian asylum seeker Reza Barati died.

The man, aged in his 20s, has spoken publicly for the first time about what he said Wilson Security guards and Transfield staff did to him in a secret compound called Chauka.

The asylum seeker making the claims said he was too scared to be named.

To protect his identity and the identity of the other detainee at the centre of the allegations, their names have been changed to Mike and Matthew.

Mike claimed he was putting himself in more danger by telling his story, but said he had to make it public.

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"We were not meant to expose it because they said to us, 'you shouldn't tell anyone. If you tell anyone we will take you to Chauka again and after getting raped we will deport you'," he said.

"But we need to expose it... I really don't care what's going to happen. If they want to kill me, threaten me or beat me... I have to expose the truth."

The secrecy surrounding the compound and what happens in it has been fuelled by the fact that it does not appear on any of the official maps of the detention centre.

It is made up of a series of converted shipping containers, each containing a single bed and no windows.

Mike said what happened to them in the secret compound was horrifying.

"I have nightmares and I have mental problems. At night time I cry because of what happened in Chauka," he said.

"I'm not lying, I have lots of panic attacks, I have anxiety. My condition is getting worse every day."

'They tied us, they beat us, they threatened us to get raped'

Mike claims the people who did this to them were employed by Wilson Security, and he can identify them by name and face.

"We were taken to Chauka. They tied us, they beat us, they threatened us to get raped and they handcuffed us to two plastic chairs," he said.

"They kept me for four days and they kept Matthew for three days. We were handcuffed and beaten. They beat us in the body to avoid bruising in the face."

Asylum seeker Reza Barati died in a riot on Manus Island on February 17. ( Supplied )

Mike and Matthew were taken to Chauka after they complained about changes to internet and phone policies that were severely hampering asylum seekers' ability to communicate with their families.

Their movement into Chuaka is not being disputed, but what happened to them while they were there is.

Mike said they signed papers under duress without being allowed to read them.

"We were shocked and asked why are you beating us? We were crying. They said 'you need to sign this piece of paper... it's about your deportation'," he said.

"We said 'we're not going to sign it'.

And they said 'if you don't sign it we're going to get locals to rape you because you are the ones who want to explain in the court and be witnesses against Australia and PNG'.

"We didn't have any other solution so we accepted it.

"If you were me you would have signed it."

Mike also alleges that while in Chauka, he and Matthew were made to sleep on muddy ground and fed only bread and water.

"You can't believe how hard that moment was for us and still I have nightmares of it," he said.

"Still I cry, I moan at night time when I'm sleeping about all the things that happened to us... and I think still our lives are in danger here.

"Lots of times the guards come and bully us and they start teasing me.

"They say things like, 'how did you find Chauka? Was it good?' And 'do you want to go again? And we'll keep an eye on you if you do anything wrong, we'll do that again'."

'Mike' wants independent investigation into allegations

Mike has called for an independent investigation into what he alleges happened to them in Chauka.

He also claims he and Matthew were not the only asylum seekers subjected to inhumane treatment while in the compound.

"Why is no one responsible for this? I know several people and some of them got beaten there - but they can't speak English," he said.

The Australian Government has confirmed Chauka's existence, but denied the asylum seekers' allegations.

"The Government rejects claims that the transferees were subjected to cruel and inhumane treatment as alleged. These are more exaggerated claims. The Minister is advised a full investigation was undertaken by Transfield with the claims being determined to have absolutely no foundation," a spokesperson for Immigration Minister Scott Morrison said.

The Government's full statement said:

The Minister has been advised the two men referred to in reports today became abusive and aggressive and were moved in accordance with operational policy within the centre. The Government rejects claims that the transferees were subjected to cruel and inhumane treatment as alleged. These are more exaggerated claims. As necessary, transferees are moved to different accommodation areas within the Manus Offshore Processing Centre (OPC) for operational reasons including for their safety and wellbeing and the safety and wellbeing of others. This can include short-term managed accommodation. Transferees in Chauka Compound have access to a shower, adequate meals and drinks, and are permitted to go to the bathroom when necessary. They also have access to health care, case managers, religious representatives, education staff and legal visits. Transferees also have access to medication as needed and are permitted to exercise, be outdoors, and access educational and reading materials. The Managed Accommodation Area is for transferees who present as a threat to others or themselves or preventing the continuance of an offence or to prevent injury or harm to themselves or others. It can also be used to provide vulnerable transferees respite or rehabilitation and time out in order to assist in the mental health and behaviour management process. The Chauka Compound is used only for as long as is necessary to prevent such events and for the shortest practicable time or to enable sufficient support. Further to our response regarding claims of human rights violations: The Minister is advised that the complaints raised with Ben Pynt are the only complaints that the department is aware of. The Minister is advised there has been no such complaints made to local authorities or service providers on site. The Minister is advised a full investigation was undertaken by Transfield with the claims being determined to have absolutely no foundation."

Ben Pynt is the director of Human Rights Advocacy at Humanitarian Research Partners, a non-profit human rights and humanitarian research organisation.

He has been in regular contact with the two asylum seekers and raised their allegations of mistreatment with the Australian Federal Police (AFP) and the office of United Nations High Commissioner for Human Rights (UNHCR).

The AFP responded to Mr Pynt by saying that Papua New Guinea police were the most appropriate law enforcement organisation to investigate the allegation.

Mr Pynt disagreed and backed Mike's calls for an independent investigation.

"The specificity of their claims is such that you couldn't make it up. Dates, times, places, people and then the documents corroborate all of those things," he said.

"It really makes me think there's no doubt.

"Quite frankly, I don't believe the Minister and neither should the Australian public. The Minister's denial has no factual basis.

"He hasn't responded to any of the individual claims and he hasn't asked an independent person to find out what happened.

"It's very simple for Mr Morrison to deny that anything has taken place.

"It's very easy for us to prove the opposite, and in the fullness of time I am confident that these claims will be borne out to be true."

Victoria Martin-Iverson, a spokesperson for the refugee rights action network in Perth, has also had regular contact with Mike, Matthew and other asylum seekers on Manus Island.

She said other detainees have also been pressured to sign documents withdrawing their witness testimony about the night Mr Barati died.

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"I have seen copies of the letter given to people who have made a statement that they would like to return home and who have also made witness statements," she said.

"In that letter they are in fact told that if they are a witness they cannot return home, and if they want to return home they need to retract their witness statements.

"So again, we have independent evidence that corroborate people's statements that they are put under some bizarre and extraordinary pressure to withdraw their witness statements regarding what they witnessed the night that Reza Barati was killed.

"I've had regular communications with both men that have made the allegations.

"The information that they give us has been consistently reliable, detailed and to date not one single allegation that they have made has been proven to be incorrect.

"They have a right like any other human being to say this happened to me.

"If it's not true, prove it's not true."