The Oslo District Court on Wednesday ruled in favor of mass murderer Anders Behring Breivik's complaint that the Norwegian state violated his human rights by keeping him in solitary confinement.

"The court decided in favor of the plaintiff on the issue regarding the European Convention of Human Rights, article 3. This relates to 'inhuman or degrading treatment or punishment,'" the court said in a statement.

Breivik sued the Norwegian government in October 2015 over his conditions in custody, which he described as "torture." The Norwegian mass murderer claimed that the state violated articles three and eight of the European Convention on Human Rights.

"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," the court said, citing the verdict.

Serving a 21-year sentence, the maximum available under Norwegian law, Breivik has so far spent his time in solitary confinement at the high-security Skien prison for murdering 77 people, mostly children, in July 2011.

While the court ruled in favor of Breivik's complaint of inhumane treatment, it said it found "no violations on the issue" concerning the "right to respect for private and family life."

According to the ruling, the Norwegian state must "pay the plaintiff's legal fees" of approximately 36,000 euros ($40,770).