The death toll from the twin attacks in Oslo a week ago rose to 77 from previously 76 on Friday, according to an updated victim name list provided by police.

The local police, who said have identified all those killed as well as the missing in the two deadly attacks, added 31 new names to the previously published list of 46, a leading Olso police official confirmed.

Norwegian police would also release an updated evaluation of threat made by extremists, said the official.

Earlier in the day, police interrogated the 32-year-old mass killer Anders Behring Breivik, whom they said was "cooperative and calm" in the process.

Several memorial services have been held in Norway and around the world in the week after the atrocity.