"The attack has become part of my identity. I value democratic values today more than before — freedom of speech, the freedom to be able to be an active politician," he told Bild am Sonntag in comments published in German.

He said those values were attacked on July 22nd, when anti-immigration extremist Anders Behring Breivik set off a bomb at Labour government offices in Oslo and then embarked on a shooting massacre at a Labour youth summer camp on an island near the capital.

"Whenever I feel sorry for myself, I recall that my concerns are very small, they are nothing compared to those of the victims," the Labour prime minister said.

He said he had "not the slightest need" to see Behring Breivik to discuss his motives.

"He killed people in my office, people whom I knew well. My wish is to leave it up to the Norwegian justice system," he said.

Prosecutors on Tuesday declared the 32-year-old criminally insane when he carried out the deadly rampage after two psychiatrists who examined him concluded that he suffered from paranoid schizophrenia.

By removing Behring Breivik's criminal responsibility, the diagnosis will probably see him sentenced to receive psychiatric care in a closed institution — possibly for the rest of his life — instead of prison.

Stoltenberg said he understood it was difficult for some of the victims' relatives to hear that the self-confessed killer might not be brought to account.

"But the best answer to the acts of July 22nd is the use of democratic values. And one of these fundamental values is the principle of the state under the rule of law," he added.

If independent judges declare him of unsound mind, it has to be accepted, he said.

Addressing the party conference of Germany's centre-left Social Democrats (SPD) in Berlin on Sunday, Stoltenberg expressed thanks for the sympathy shown Norway after the twin attacks.

Referring to events in Norway and Germany, he said extremism was developing in very different forms.

Following the revelation of a neo-Nazi cell in Germany believed to have murdered 10 people, mainly shopkeepers of Turkish origin, the SPD delegates adopted a resolution saying sorry to relatives of the victims.