"We have confirmation that at least 80 people are dead. We do not exclude a higher toll," said Are Frykholm, speaking of the massacre at a youth camp on the island of Utoeya. Seven others died in a powerful bomb blast in central Oslo.
Earlier reports said at least 10 people died in the island while seven perished in a bombing in central Oslo.
The bombing in the heart of the capital, where the prime minister's office and several government buildings are located, also left nine people critically injured.
The gunman has been identified as a 32-year-old Norwegian. According to the TV2 channel, he has links to right-wing extremists and possessed two weapons registered in his name.