Norway's district court ruled that Breivik, an anti-Muslim neo-Nazi who killed 77 people, must stay in prison.

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

Last month Breivik faced a parole hearing where he professed to having white supremacist views and flashed Nazi salutes, while claiming to have renounced violence.

Breivik killed eight people with a car bomb in Oslo before gunning down 69 people, most of them teenagers, at a Labour Party youth camp in July 2011.

He is serving Norway's maximum sentence of 21 years, which can be extended indefinitely if he is deemed a continued threat to society.

However, he was eligible to seek parole after serving the first 10 years of his term, and is entitled to apply for release a year after each rejection.

Breivik's lawyer, Oystein Storrvik, said his client should be released to prove he is reformed and no longer a threat to society, which he said was not possible to prove while he is in total isolation.

Mr Storrvik called it "a paradox that a person is treated so badly in prison that he never gets better... he never gets out".