Norwegian police on Tuesday found and destroyed more explosives in the farm of the gunman behind last week's twin attacks in Norway.

Police said they found the explosives in the farm rented by self-confessed killer Anders Behring Breivik in the village of Asta of Hedmark county.

They did not give any information about the type of the explosives or when they were found, only saying they considered it better to blow up the explosives on the spot rather than move them.

Breivik had confessed in a Monday court hearing to a bombing in downtown Oslo on Friday, killing eight people and rocking Norwegian government quarters, and a shooting rampage in the Utoeya island which claimed 68 more lives later the same day.

He was put into a eight-week detention, twice the normal limit, ordered by the Oslo district court on Monday to facilitate investigations of the twin attacks.

Police and prosecution were considering whether Breivik could be charged with crimes against humanity, the maximum sentence for which is a 30-year prison term.