Norwegian mass killer Anders Behring Breivik complained at a court hearing that keeping him in solitary confinement in prison was a form of "torture" after a judge ordered that he remains in isolation for another four weeks.

Breivik, who has admitted killing 77 people on July 22, has been kept in isolation for two months.

Under Norwegian law, solitary confinement can only be imposed for four weeks at a time, but the prosecution is free ask for an extension when the term runs out, Reuters reports.

Eight of Breivik's victims were killed in a bombing in Oslo that destroyed the Norwegian government's headquarters and 69 were gunned down on a nearby island.

Judge Anne Margrethe Lund said the isolation was necessary to hinder Breivik from communicating with potential accomplices, whose existence the police need to investigate further.

Lund said she had stopped Breivik from speaking at length at the hearing as his topic was deemed irrelevant.

"He wanted to communicate something to the court, but that wasn't relevant to the decision the court was to make today, so therefore he was not allowed to explain further regarding that issue," Lund told a news conference.

The judge said Breivik had repeated a previous statement that he experienced his isolation as a "form of torture."

Breivik's lawyer Geir Lippestad told reporters Breivik asked to read a statement at the closed-door hearing and had shown no signs of regret for his deeds.

"He has not expressed any remorse," he said. "He appeared calm and restrained as he had been earlier."

"He said a few words about how he saw custody and isolation. He said it is tough to be in isolation," Lippestad said.

Legal experts expect Breivik to remain in prison until trial, possibly in the first half of 2012, although he will not necessarily stay in solitary confinement that long.

Police were guarding the courthouse with machine guns and fingers on the trigger, highlighting the tension surrounding the proceedings in a country where armed police is a rare sight.