Norwegian mass killer Anders Behring Breivik gestures as he arrives at the court room in Oslo Courthouse August 24, 2012.[Agencies]

OSLO - A Norwegian court found Anders Behring Breivik sane on Friday and gave him a maximum jail term for murdering 77 people in a shooting and bombing last year, offering closure to a Nordic nation devastated by its worst attack since World War Two.

Breivik, who has admitted blowing up the Oslo government headquarters with a fertiliser bomb, killing eight, before gunning down 69 at the ruling party's summer youth camp, was sentenced to 21 years in prison, the maximum penalty in Norway.

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But officials can prevent his release indefinitely and are expected to do so if the anti-Muslim right-winger still poses a threat. Breivik had rejected prosecutors' arguments that he was mad, and had said he would appeal if he were ruled insane.

"In a unanimous decision ... the court sentences the defendant to 21 years of preventive detention," said judge Wenche Elizabeth Arntzen, dismissing the prosecutor's call for a verdict that would have labelled Breivik insane and have confined him indefinitely to psychiatric care.

The killings shook this nation of five million which had prided itself as a safe haven from much of the world's troubles, raising questions about the prevalence of far-right views in a country where oil wealth has attracted rising immigration.

Breivik, 33, will be kept in isolation inside Ila Prison on the outskirts of Oslo inside relatively spacious quarters that include a separate exercise room, a computer and a television.

Criminal guilt was never an issue as Breivik acknowledged and described in horrific detail his murders. His 10-week trial focused on his sanity, with prosecutors arguing he should be declared insane and held in a mental hospital, not jail.

For many survivors the actual verdict was academic. But the trial that went into every detail of the day-long killing spree, Norway's worst massacre since the Second World War, offered some closure for families.

Some survivors wanted a sane verdict, which makes clear that Breivik is responsible for his actions and also makes a protracted appeal unlikely.

Breivik has described an insane verdict as "a fate worse than death". Were he to have been found insane and decided to appeal, the entire trial would have had to be repeated.

Breivik justified his killing spree arguing that the centre-left Labour party is deliberately destroying the nation by encouraging Muslim immigration.