An Oslo court on Friday ordered a new psychiatric evaluation of Anders Behring Breivik, who killed 77 people in twin attacks in July, after an earlier and widely contested test found him criminally insane.

"Due to the gravity of this case, the criminal responsibility (of Behring Breivik) must be examined again," Oslo District Court judge Wenche Elizabeth Arntzen told a news conference.

Two new experts, Agnar Aspaas and Terje Toerrisen, were named to evaluate the 32-year-old rightwing extremist's sanity.

In late November, two court-appointed psychiatrists concluded that Behring Breivik was suffering from paranoid schizophrenia and should be considered criminally insane and therefore not accountable for his actions.

If the finding is confirmed, Behring Breivik, who has confessed to carrying out the deadliest massacre on Norwegian soil since World War II, would likely be sentenced to psychiatric care in a closed ward instead of prison.

The initial report, later supported by an expert panel, was controversial in Norway, with critics pointing to the years of detailed planning Behring Breivik had put in and cool, methodic execution of the massacre.

On July 22, Behring Breivik first set off a car bomb outside government buildings in Oslo, killing eight people.

He then went to Utoeya, some 40 kilometres (25 miles) northwest of Oslo, and, dressed as a police officer, spent more than an hour methodically shooting and killing another 69 people, mainly teens, attending a summer camp hosted by the ruling Labour Party's youth wing.