Norwegians are marking the first anniversary of twin attacks that killed 77 people, the worst atrocity carried out in the country since World War II.

Religious services, wreath-laying ceremonies, commemorative gatherings and a concert are scheduled across the country on Sunday, a year after 33-year-old Anders Behring Breivik set off a bomb near government building in Oslo and then went on a shooting rampage on nearby Utoeya Island.

Speaking to Al Jazeera, Norwegian Prime Minister Jens Stoltenberg says Breivik "succeeded in killing many people and causing damage and sorrow but failed to change Norway".