A new psychiatric examination has found that confessed mass killer Anders Behring Breivik is not criminally insane, despite a claim based upon an earlier assessment.

Tuesday's finding comes six days before the 33-year-old Norwegian is set to stand trial on terror charges a bomb and shooting rampage that killed 77 people over the summer.

The new psychiatric conclusion conflicts with a previous examination that diagnosed Breivik as psychotic. The initial probe found the confessed killer was suffering from "paranoid schizophrenia".

That diagnosis prompted prosecutors in the case to say Breivik should be committed to a mental institution rather than prison, if convicted.

Breivik has confessed to the attacks but denies criminal guilt. He claims the attacks were necessary in what he calls a civil war against Islam in Europe.