SKIEN, Norway -- Norwegian mass murderer Anders Behring Breivik told a court Thursday that his isolation in prison had deeply damaged him and caused him to be even more radicalized.

The 37-year-old right-wing extremist, who murdered 77 people in a 2011 bomb attack and shooting rampage, is serving a 21-year sentence in a high-security prison in southern Norway, where his correspondence is monitored. He has been in solitary confinement since his sentencing in 2012 and has limited access to visitors, mostly by prison personnel, medical staff and a priest.

Dressed in a black suit and tie, the stone-faced Breivik spoke coherently without emotion, saying he agreed with government attorneys who had warned that the self-proclaimed neo-Nazi had become more radicalized in prison.

“I have been damaged by the isolation ... (and) radicalization has been a consequence of it,” Breivik said before a three-judge panel which is reviewing a government appeal against a ruling that his isolation in prison violates human rights. “I have not been a little hurt, I have been very damaged.”

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Saying he felt locked in a bubble, Breivik complained about the lack of personal contacts. He is allowed to receive visits from family and friends, but hasn’t received any except from his mother before she died.

Breivik was speaking during a hearing reviewing a government appeal against a ruling that his isolation in prison violates human rights.

Last year, Breivik sued the government, arguing that his solitary confinement, frequent strip searches and often being handcuffed in the early part of incarceration violated his human rights.

In a surprise decision, the Oslo District Court in April sided with his claim, finding that his isolation was inhuman and degrading and breached the European Convention on Human Rights, and ordered the government to pay his legal costs.

But it dismissed Breivik’s claim that his right to respect for private and family life was violated by restrictions on contacts with other right-wing extremists, a decision that Breivik in turn is appealing.

The government maintains that Breivik is dangerous and must remain isolated from inmates in the high-security prison in Skien, where the appeals case is also being heard.

Breivik’s lawyer Oystein Storrvik said the control over his communications with the outside world amounts to a “blatant breach of human rights,” arguing that frequent censorship of his letters and long review periods means Breivik cannot keep regular communication with people outside of the penal system.

Attorney General Fredrik Sejersted, representing the government in the appeal, said Breivik continues to spread extremist ideology through his writings, and that all his correspondence should still be monitored and his letters opened. He told the court that Breivik continues to try to find ways of bypassing censorship of his correspondence, including an ad to find a marriage partner.

Sejersted also said that Breivik’s prison conditions are better than for many other inmates. He has a three-cell complex where he can play video games, watch TV and exercise, in compensation for his solitary confinement. He is served coffee and newspapers in the morning, often plays video games on the Xbox console, watches movies and spends much time studying.

Sejersted said Breivik was still “very deeply engaged in his political right-wing, extremely neo-Nazi project,” and should remain isolated.

At the time of the attacks, Breivik claimed to be the commander of a secret Christian military order plotting an anti-Muslim revolution in Europe, but now describes himself as a traditional neo-Nazi who prays to the Viking god Odin.

Six days have been reserved for the hearings by the Borgarting Court of Appeals in the makeshift courtroom in the gym of the prison in Skien, 135 kilometers (85 miles) southwest of the capital, Oslo. They are scheduled to end Jan. 18, with a ruling expected in February.