A Norwegian court ruled Tuesday that far-right extremist Anders Behring Breivik, who killed 77 people in 2011, must remain in prison, saying there remains "an obvious risk" he could return to behaviour that led up to the massacre. 

Last month, Breivik faced a parole hearing before the three-judge Telemark District Court where he professed white supremacist views and flashed Nazi salutes on the hearing's opening day, while claiming to have renounced violence. 

But the court said he remains a potential threat. 

"Because his psychiatric condition is unchanged, there is an obvious risk that he will fall back on the behaviour that led up to the terrorist acts on July 22, 2011," the court said in its ruling. 

He "used extreme violence as a tool to achieve his own political goals" and the court "has no doubt that [Breivik] still today has the ability to commit new serious crimes that may expose others to danger". 

Breivik is serving Norway's maximum 21-year sentence for setting off a bomb in Oslo's government district and carrying out a shooting massacre at a summer camp for left-wing youth activists. 

Among the victims was New Zealand-born Sharidyn Svebakk-Bohn, 14. 

Breivik was declared sane at his trial, although the prosecution argued that he was psychotic. He didn't appeal his sentence but unsuccessfully sued the government for human rights violations for denying him the right to communicate with sympathisers. 

Breivik could be held longer than 21 years under a provision that allows authorities to keep criminals in prison for as long as they're considered a menace to society. 

During last month's hearing, prosecutor Hulda Karlsdottir argued Breivik still is "a very dangerous man" and "has not shown any genuine remorse in court". 

Norwegian news agency NTB quoted Karlsdottir welcoming the ruling as "well founded". 

A psychiatrist who has observed Breivik since 2012, testified that he can't be trusted while a prison official told the hearing "there is an imminent danger" that, if released, Breivik would again commit serious crimes. 

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

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

Tuesday's ruling can be appealed. Norwegian broadcaster TV2 cited Storrvik saying Breivik would appeal the ruling. The lawyer was not immediately available for comment. 

- By Jan M. Olsen of AP