"Norway is today more imbued with democracy and diversity than it was on July 22, 2011," Stoltenberg told the German daily Sueddeutsche Zeitung in an interview published Saturday.

Breivik's bombing in Oslo and his subsequent rampage on the island of Utoeya claimed 77 lives that day.

The attacks prompted record numbers of people to join political organisations and youth groups, Stoltenberg said.

Democracy is "the most important weapon in the fight against violence," he added.

Breivik maintained that his attacks were necessary to defend Norway, a normally quiet country known for its tolerance and quality of life, against multiculturalism and a "Muslim invasion."

He has not denied the killings, but pleaded not guilty and wants the court to find him of sane mind to show that political extremism, not psychosis, was behind his actions.

Breivik told the court on the closing day of his trial a month ago that he "carried out a small barbarism to stop a greater barbarism."

His rampage on Utoeya island targeted a summer camp of the ruling Labour Party's youth wing.