Amnesty International has accused the Nauruan government of trying to avoid public scrutiny of the treatment of asylum seekers on the Pacific Island.

Amnesty says the Nauruan government has declined a request to tour the Australian-run immigration detention centre, citing "the current circumstances" and it being "an incredibly busy time".

Amnesty's refugee spokesman Graham McGregor says the human rights group wanted to view conditions at the Nauru centre, which currently houses 1,177 asylum seekers including women and children.

"It is extremely unusual for us to be denied access to a detention centre and in fact we visited the Manus Island detention centre, as you might recall, back in November last year," he said.

"So we, as part of that work, similarly put in a request to visit the Nauru detention centre and we received a refusal."

Amnesty International's Manus Island report, which was published in December, described conditions in the PNG centre as cruel, inhuman, degrading and violating prohibitions against torture.

"We have good reason to believe there may be similar human right abuses taking place in Nauru," Mr McGregor said.

"Certainly what has leaked out about the Nauru detention centre has been extremely concerning, particularly the recent allegations of water shortages and allegations that children at the facility are being physically abused."

Amnesty says it's is being 'cold shouldered'

Amnesty International says the request to visit the detention centre was put to the Nauru justice minister David Adeang in early March.

He says the minister responded that the Nauru processing centre "was incredibly busy and that they felt that a visit by Amnesty International at this time may appear premature".

A proposal for alternative dates was ignored, according to Mr McGregor, and "enough time has passed that we would feel we are being cold shouldered."

He has accused Nauru of trying to hide conditions for the asylum seekers.

"[The refusal] did follow some other steps that have been taken recently by the Nauruan government to try and prevent public scrutiny of conditions inside the detention centre," he said.

"For example, back in February of this year, the Nauruan government increased the visas for journalists to visit the country from $200 to $8,000, which was a pretty clear sign they simply didn't want people coming and reporting on what was going on there.

"We did have a little hint there that the Nauru government was not comfortable with that sort of scrutiny, but again we were still surprised by their response."

Mr McGregor says he does not accept that it is too busy at the centre for an Amnesty International inspection.

"I would imagine conditions at these detention centres are always pretty busy," he said.

"They are very crowded, they are handling a very difficult system, a very difficult population of people who have a lot of mental health problems, a lot of existing trauma, a lot of health conditions.

"On Nauru, of course, you have children and pregnant women there as well. It is always going to be a busy time."

UN human rights inspectors' invite withdrawn

Amnesty's rejection comes after the Nauruan government withdrew an invitation for a team of UN human rights observers.

Human rights inspectors from the United Nations Working Group on Arbitrary Detention had wanted to investigate the conditions of the asylum seekers sent by Australia, but had to cancel at the last minute.

The Nauru government questioned whether the UN team was trying to use the Pacific island nation as a publicity stunt.

A government spokesman told the ABC earlier this month that, "given the way they have gone about this, it is reasonable to question whether this is merely another publicity stunt by a group with a political agenda".

The ABC has been told the first refugee determinations at Nauru's offshore immigration processing centre are now a couple of weeks away.

The asylum seekers are being told that people found to be refugees will be settled in Nauru on a visa for a period up to five years.

They are being warned not to break any laws or take part in protests while awaiting a decision.

While the first refugee determinations are due to be handed down soon, the detainees are being urged to be patient.

Amnesty International says it will keep asking Nauru for access to the immigration processing centre.

The ABC has sought comment from the Nauruan government.

A spokesperson for Australia's Immigration Minister Scott Morrison said: "We are not aware of any such decisions (on rejection of access), we have not been consulted on any such decisions, and this is ultimately a matter for Nauru."