Norway has been hit by twin attacks on July 23 - a massive bomb blast in the capital and a shooting attack on young people at a governing Labour Party youth camp.
At least seven people were killed in the bombing, which inflicted huge damage on government buildings in Oslo.
A few hours later a gunman opened fire at the camp on an island outside Oslo, killing at least 10.
The suspected gunman was arrested at the camp and the government have confirmed that he is Norwegian.
Police have said the 32-year-old suspect was also linked with the bomb attack.
Witnesses described the gunman as tall, blonde and say he was dressed as a policeman.
Prime Minister Jens Stoltenberg, whose Oslo offices were among those damaged by the bomb, described the attacks as "bloody and cowardly".
He said Norway had been "shaken by evil" but that Norwegian democracy and ideals would not be destroyed.
"We are a small nation and a proud nation. No-one will bomb us to silence, no-one will shoot us to silence," he said in a televised address.
No group has claimed responsibility for the attacks.
Several people from the camp are still missing and rescue teams have been scouring the waters around the island after dead bodies were reportedly seen in the water.
BBC
