Norway on Sunday held a grand national memorial ceremony honoring the 77 victims of the twin attacks on July 22, as the Nordic country struggles to move on from last month's atrocity.

A boy blows soap bubbles at the Oslo Cathedral as people pay their respects to those killed in last month's bomb and shooting attack in Oslo August 21, 2011. [Photo/Agencies]

Addressing over 6,000 people who gathered in Oslo's Spektrum arena for the candle-lit memorial service, Norwegian King Harald V told the nation of 5 million people that Norway would surmount its pain.

The king said that it was his firm belief that Norwegians would continue to live "freely and openly" after what had happened a month ago.

Among the 6,000 people present at the arena were relatives of the victims, survivors, police and emergency personnel who dealt with the two deadly attacks, the worst in Norway since World War II.

Norwegian Crown Prince Haakon, Finnish President Tarja Halonen, Icelandic President Olafur Grimsson, Swedish Crown Princess Victoria and Denmark's Crown Prince Frederik, also attended the ceremony, joined by Norwegian Prime Minister Jens Stoltenberg and his counterparts from Denmark, Finland, Iceland and Sweden.

After performances dedicated by Norwegian artists, the names of all the 77 victims were read at the ceremony, which started at 3 pm local time (1300 GMT) amid tightened security.

Flags flew at half-staff over the royal palace, the parliament building and government buildings.

Sunday's event marks the end of an official period of mourning for the 77 victims, mostly youths, who perished in the twin attacks by Anders Behring Breivik.

Breivik, a 32-year-old Norwegian, has admitted that he set off a truck bomb in downtown Oslo and then went on to a shooting spree at a Labor Party youth camp on the island known as Utoeya, some 40 kilometers to the northwest of Oslo.

He was arrested on the island 90 minutes after he fired his first shots.

An Oslo court decided earlier this week to extend his isolation detention by another four weeks.