"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 Tørrisen, were named to evaluate the 32-year-old right-wing extremist's sanity "before the beginning of (his) trial" on April 16th.
Behring Breivik on Friday refused through his lawyer to cooperate with the probe.
"He feels the first report was 80-percent wrong," his lawyer Geir Lippestad said after informing his client of the judges' decision.
"He doesn't think the experts have the knowledge necessary to understand him," Lippestad told reporters outside the high-security Ila prison near Oslo where Behring Breivik is currently being held.
Given his unwillingness to interact, the self-confessed killer could be moved from prison to a psychiatric institution for observation.
"Forced committal could be necessary. But that is something we will have to discuss with the court," one of the two new experts, Aspaas, told the NTB news agency.
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.
In their 243-page report, the two experts who carried out the first probe painted a picture of a person with "grandiose illusions," incapable of living in society and believing he was destined to determine who should live and who should die.
If that 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 his cool and methodical execution of the massacre.
On July 22nd, the man who has claimed to be on a crusade against multi-culturalism and the "Muslim invasion" of Europe, first set off a car bomb outside government buildings in Oslo, killing eight people.
He then went to Utøya island, some 40 kilometres north-west 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.
While acknowledging the criticism that followed the first probe, Arntzen insisted on Friday the decision to order a new evaluation "does not imply any criticism of the first experts' report."
She justified the court order by stressing "the necessity to clarify this case as much as possible."
Amid the controversy over the initial expert conclusion, also criticised by Behring Breivik himself, several lawyers representing survivors and family members of the victims had requested a new evaluation.
The criticism flared further when Norwegian media earlier this month revealed that three psychologists and one psychiatrist who have been monitoring Behring Breivik in prison had not detected signs that he was psychotic and did not believe he was in need of medical treatment.
"This is an intelligent decision made by an intelligent judge," said lawyer Mette Yvonne Larsen, who headed the call for a new psychiatric evaluation.
"It cannot hurt to cast more light on this case," she told AFP on Friday.
Neither the defence nor the prosecution had meanwhile wanted a new psychiatric evaluation.
At the end of the day, it will be up to the Oslo court to determine if Behring Breivik should be considered criminally insane or not during his trial.