Norwegian authorities are looking into the possibility of carrying out another psychiatric examination of mass killer Anders Behring Breivik after a review commission approved a finding that he was insane and unfit for prison.

Breivik killed 77 people on July 22 when he planted a car bomb that killed eight people at an Oslo government building, then went on to shoot dead 69 more, most of them teenagers, at an island summer camp of the ruling Labor Party's youth wing.

A November 29 psychiatric report concluding that the anti-Islam militant was insane was approved Thursday by a medical review commission, strengthening the likelihood he will avoid a prison term.

Later Thursday, a judge asked prosecutors and defence lawyers to decide if they wanted another examination.

The court asks the parties to comment on whether it would be desirable for the court to appoint new experts to undertake a judicial-psychiatric examination, Oslo District Court Judge Anne Margrethe Lund said in a letter issued publicly.

The seven-member commission told the court it had no significant comments to the initial report by two court-appointed psychiatrists who diagnosed Breivik as psychotic.

State broadcaster NRK reported Wednesday that three of the review panel's members had big objections to the initial report declaring Breivik criminally insane, but Thursday's commission statement gave no such indication.

A court official said Breivik in any case faces a trial date in April, and the trial judge will remain free to order a new examination at any time.

(Reporting by Walter Gibbs Editing by Maria Golovnina)