SKIEN, Norway (AP) — A Norwegian court on Tuesday is reviewing a government appeal against a ruling that the isolation of mass murderer Anders Behring Breivik was inhumane and violates his human rights.

The 37-year-old right-wing extremist, who killed 77 people in a bomb and shooting rampage in 2011, sued the government last year, saying his solitary confinement, frequent strip searches and the fact that he was often handcuffed during the early part of his incarceration violated his human rights.

In a surprise decision in April, the Oslo District Court sided with Breivik's claims that his isolation in the maximum security Skien prison breaches the European Convention on Human Rights.

It ruled that "the prohibition of inhuman and degrading treatment represents a fundamental value in a democratic society. This applies no matter what — also in the treatment of terrorists and killers." It also ordered the government to pay Breivik's legal costs of 331,000 kroner ($41,000).

However, it dismissed his claim that his right to respect for private and family life was violated by restrictions on contacts with other right-wing extremists.

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. Legal experts say he will likely be locked up for life.

He is being held in isolation in a three-cell complex where he can play video games, watch TV and exercise. He has also complained about the quality of the prison food, having to eat with plastic utensils and not being able to communicate with sympathizers.

The government has rejected his complaints, saying he is treated humanely despite the severity of his crimes and that he must be separated from other inmates for safety reasons.

Breivik had carefully planned the attacks on July 22, 2011. He set off a car bomb outside the government headquarters in Oslo, killing eight people and wounding dozens. Dressed in a police uniform, Breivik then drove to the island of Utoya, about 40 kilometers (25 miles) away, where he opened fire on the annual summer camp of the left-wing Labor Party's youth wing. Sixty-nine people there were killed, most of them teenagers, before he surrendered to police.

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

The massacre shocked the oil-rich, quiet Scandinavian country and many feel Breivik has had too much attention and visibility.

The appeals case opens in a makeshift courtroom in the gym of Skien prison in southern Norway, where Breivik is incarcerated. Six days have been reserved for the hearings before the Borgarting Court of Appeals hands down a verdict in the case.