A ban on Facebook in Nauru was implemented at the request of the Australian Government to assist its Cambodian resettlement policy, a refugee advocacy group says, citing an anonymous source.

Nauru opposition MP Matthew Batsiua said Facebook users in Nauru discovered on Thursday they had been denied access to the social media site.

He said it was an attempt by the Nauru government to prevent free speech and curb any criticism it faces.

Pamela Curr from the Asylum Seeker Resource Centre said that one of her contacts within the Nauruan community told her the Australian Government was behind the ban.

"My contacts are telling me that this was done at the request of the Australian Government," Ms Curr told Radio Australia's Pacific Beat program.

"They said that the Australian Government is anxious to get a group of people going to Cambodia and they are concerned that the people on Nauru are in contact with advocates in Australia who they believe are talking them out of the Cambodian option."

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She said she was in no doubt about the claim and said she believed Facebook would stay blocked there until refugees were flown to Cambodia.

"I was very surprised to hear this but I have no doubt, and we have been assured that once the plane leaves for Cambodia that the Facebook blocking will be lifted," she said.

The Department of Immigration and Border Protection told the ABC that "any internet restrictions in Nauru are a matter for the government of Nauru".

The Nauru government last week said it was restricting internet access to block pornography, especially child pornography.

In a statement issued to explain the ban, the government said "pornography is not consistent with the faith and values" of the people of Nauru.

The country's only internet service provider, Digicel said in a statement the Nauru government "instructed the blocking of certain internet sites".

The company said some sites had already been blocked while the government was "evaluating their suitability".

A spokeswoman for Facebook said the site was aware of reports that people in Nauru could not access Facebook.

"We believe that restricting access to a free and open internet deprives people of important economic and social opportunities and choices and hope that access will be restored soon," she said.

The ABC has attempted to contact the Nauru government.