MASS murderer Anders Behring Breivik is in touch with fellow right-wing extremists from behind bars and must to be held in solitary confinement, a government lawyer has said.

During an appeal against a court ruling last year that Breivik’s isolation in prison violates the Norwegian’s human rights, Attorney General Fredrik Sejersted said that the self-proclaimed neo-Nazi continues to spread extremist ideology through voluminous writings. Sejersted added that the terrorist’s correspondence should be monitored, including opening his letters.

The government maintains Breivik, who killed 77 people in a bomb-and-shooting rampage, is dangerous and should be isolated from inmates. The hearings are expected to end by the end of next week, with a verdict expected in February.

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

In a surprise verdict, the Oslo District Court sided with Breivik's claims, finding that his isolation was "inhuman [and] degrading", breaching the European Convention on Human Rights - and ordered the government to pay Breivik's 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.

Sejersted told the court that Breivik continues to try to find ways of bypassing censorship of his correspondence, including in an ad to find a marriage partner.

"The text is structured like a personal ad because he knows that personal ads have special protection in Strasbourg", which holds the seat of the European Court of Human Rights.

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.

The terrorist arrived in court quietly, dressed in a black suit, with shaved head and sporting a beard grown since last year's court appearance.

Stone-faced, he glared at reporters briefly before being seated. He refrained from making a Nazi salute as he did on the first day of the hearing when he was admonished by the judge.

Breivik was convicted of mass murder and terrorism in 2012 and given a 21-year prison sentence that can be extended for as long as he's deemed dangerous to society.

At the time of the attacks, he 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.

He also made a Nazi salute to journalists at the start of his human rights case last year.