A district court in Norway on Tuesday ruled that Anders Behring Breivik, an anti-Muslim neo-Nazi who killed 77 people, must remain in prison.

Breivik killed eight people with a car bomb in the Norwegian capital Oslo before shooting 69 people, mainly teenagers, at a Labour Party youth camp in July 2011.

The district court in Telemark was unanimous in its verdict denying Breivik's request for parole having served the first 10 years of his sentence.

In 2012, Breivik was sentenced to 21 years in prison, the country's maximum sentence which can be extended for as long as he remains a threat to society.

"The risk of violence is real and significant and equal to what it was when (Breivik) was first sentenced," the court said.

Breivik's lawyer, Øystein Storrvik, said the 42-year-old should be released to prove he is reformed and no longer a threat to society. This, Storrvik added, was not possible while his client remained in complete isolation.

The prosecutor, Hulda Karlsdottir, however, argued Breivik remained a "very dangerous man" and has not shown "any genuine remorse" in court.

Breivik is entitled to apply for release a year after each request for release is dismissed.

(With input from agencies)