A bombing and shooting that left at least 91 dead on Friday is "a national tragedy" and the worst act of violence in Norway since World War II, Prime Minister Jen Stoltenberg said Saturday.
The bombing of government buildings in Oslo on Friday, and a subsequent shooting spree at a political youth camp, have so far claimed 87 lives, police said.
Stoltenberg said he had been due to address the youth camp at the Utoya island, organized by the youth league of his Labor Party later Saturday. "For me, Utoya was the paradise of my youth, now it has become hell," Stoltenberg said.
Both he and Justice Minister Knut Storberget, who also attended the news conference, said it was too early to comment on the possible motive of the acts or if they were conducted by only person.
On Friday, a gunman dressed in police uniform opened fire at a youth camp of Norway's ruling political party, killing at least 84 people, hours after a bomb killed seven in the government district in the capital Oslo.
Witnesses said the gunman, identified by police as a 32-year-old Norwegian, moved across the small, wooded Utoeya holiday island firing at random as young people scattered in fear. Norwegian television TV2 said the gunman detained by police was described as tall and blond and had links to right-wing extremism.
Police seized the gunman, named by local media as Anders Behring Breivik, and later found undetonated explosives on the island, a pine-clad strip of land about 500 meters long, to the northwest of Oslo.
Breivik's Facebook page appeared to have been blocked by late evening. Earlier it had listed interests including bodybuilding, conservative politics and freemasonry.
Norwegian media said he had set up a Twitter account a few days ago and posted a single message on July 17 saying: "One person with a belief is equal to the force of 100,000 who have only interests."
About 10 police officers were outside the address registered to his name in a four-story red brick building in west Oslo.
The Norwegian daily Verdens Gang quoted a friend as saying he became a right-wing extremist in his late 20s. It said he expressed strong nationalistic views in online debates and had been a strong opponent of the idea that people of different cultural backgrounds can live alongside each other.