The Nauruan government’s censorship of Facebook will be temporary and only until “necessary protection mechanisms” are put in place to stop “criminals and sexual perverts”.

A briefing paper from the Nauruan government obtained by Guardian Australia is the first official acknowledgment that Facebook has been restricted on the island.

It said an internet ban on some sites was permanent and had been months in the making after concerns about images of child sexual abuse being distributed.

But opposition members of the Nauruan parliament have raised concerns about the restrictions, which they said were designed to prevent the flow of information to Nauruans and from asylum seekers held in Australia’s immigration detention centre.

The briefing paper said: “As you are aware certain internet sites have been heavily restricted. These are sites that contain or have been maliciously used to publish and broadcast explicit, obscene or pornographic material. This decision has been made by government in its efforts to protect its people from the abuse of the internet which has seen vulnerable individuals, especially young Nauruan girls, being maliciously targeted, harassed and even bullied.

“The decision was not made overnight but over a period of several months of investigation, consultation and outreach to sites to rectify what is on their part neglect of protection afforded to the Nauruan people, particularly our women and children.”

It said the block on Facebook – which was widely used by Nauruans to find news about the country in the absence of local press reports, and by asylum seekers – was only temporary.

“Other sites such as Facebook that have been abused by malicious users are under temporary restriction until the necessary protection mechanisms are in place to ensure that Nauruans and members of our community are not left exposed and vulnerable to the actions of criminals, sexual perverts and cyber bullies,” it said.

It is not clear how blocking Facebook would prevent the distribution of offensive material, how long the site would continue to be blocked, or what additional protection measures would be put in place. Facebook has policies surrounding the sharing and distribution of inappropriate material that it applies to suspend users who are found to be in breach.

The Nauruan government has not responded to requests for comment on blocking the site.

A spokeswoman for Facebook said: “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.”

The Facebook ban was directed by the Nauruan government, but was imposed by the nation’s internet provider, Digicel. It came shortly after the general manager’s visa was cancelled and she was replaced by another Digicel staff member.

Opposition members of the Nauruan parliament have expressed concern about the censorship in Nauru. The former president, Sprent Dabwido, said the block was imposed due to “paranoia” about independent media scrutiny on the island nation.