A Norwegian court on Friday ordered that the man who killed 77 people in twin attacks in July should undergo psychiatric observation to determine his mental state before his trial begins.

A near-constant monitoring of 32-year-old right-wing extremist Anders Behring Breivik "should provide precious information that would be difficult to obtain in another manner," the Oslo district court ruled.

Late last year, a first examination by two court-appointed psychiatrists concluded that Behring Breivik was a paranoid schizophrenic, and therefore criminally insane.

Following widespread criticism of that conclusion, the court ordered a new evaluation.

The confessed killer cooperated with the first experts but has refused to speak with the two new experts, who requested at the end of January he be temporarily committed to a psychiatric hospital.

Even though he said he objected to 80 percent of the first psychiatric evaluation, Behring Breivik has opposed both the new probe and being under observation.

On Friday, the court gave the green light for him to placed under observation for four weeks, but rejected the experts' request to commit him to the Dikemark hospital southwest of Oslo.

They said he should instead be committed for mandatory observation at the high-security Ila prison where he is being held.

That means specialists from Dikemark will need to work at the prison, observing Behring Breivik's behaviour for large parts of each day.

The two court-appointed experts will then use their notes to reach a conclusion by the April 10 deadline, less than a week before the trial is set to begin on April 16.

On July 22, the man who has claimed to be on a crusade against multi-culturalism and the "Muslim invasion" of Europe set off a car bomb outside government buildings in Oslo, killing eight people.

He then went to Utoeya island, 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.