In a letter sent to Norway's Dagbladet newspaper, Breivik claimed that he had sent no fewer than 87 copies of the censored letter to various newspapers, television broadcasters and other individuals and organisations.
"Will you never truly accept that they are 'burying me alive'?" Breivik wrote in his letter to Dagbladet. "Do not you see that this would be an admission of failure for everything that you claim to believe in ?"
According to Breivik, this is the first time that one of his letters to has been prevented from reaching the media, although correspondence with other individuals and groups has previously been stopped.
In his letter, Breivik includes from what he claims is the formal decision made by the prison authorities.
“The prisoner wishes to send out a joint letter to several media companies, government agencies, organisations, and individuals," he quotes. "The letter has been stopped due to its content...content that, seen in the context of the prisoner's manifesto, actions, and use of symbolism, could incite disruption of peace, order, and security.”
In December last year, Norway's prison authorities admitted that they had blocked several of Breivik's letters to prevent him from setting up a political network outside the prison gates.
"We have refused to send some letters from Breivik for reasons of security. We're talking about roughly 220 letters," Yling Faeste, a spokesman for the prison administration, told AFP.
"We control his communication, and he is not allowed to set up a network that could commit even more crimes."
Since Breivik's bombing of Oslo's government district that killed eight people and attack on the Labour Party youth camp on the island of Utøya, where he shot dead another 69, he has been kept in strict isolation with no contact with other prisoners.
Breivik claims that his prison conditions are in violation of the European Convention of Human Rights and has recently filed a lawsuit against the Norwegian state.
Øystein Storrvik, Breivik's lawyer, confirmed that letters have been stopped by the prison authorities.
“This will be a topic in the lawsuit against the state. This type of censorship is problematic and a matter of principle, especially as the letters were addressed to large Norwegian media companies," he told Dagbladet.
“His isolation is by far the most important issue in the lawsuit, but we think that communication with major Norwegian media should not be censored.”