Anders Breivik, the man who has confessed to killing scores of people in a shooting spree and bombing in Norway, has claimed "two more cells" were working with him.

The 32-year-old made the claims before a closed court hearing on Monday, where he also admitted carrying out the attacks but entered a plea of not guilty.

He told the court he wanted to save Norway and Western Europe from "cultural Marxism", and accused the Norwegian Labour party of allowing "mass imports of Muslims" into the country, Judge Kim Heger said.

The judge added that Breivik's claim about further cells would have to be investigated. Breivik had previously told police that he acted alone.

"The accused has made statements today that require further investigation, including that 'there are two more cells in our organisation'," Heger said.

Meanwhile, police revised down the killings at the Labour camp party on the island of Utoeya to 68, and increased the death toll from the bomb blast in central Oslo to eight, bringing the total to 76.

Speaking to reporters, officers said Breivik appeared calm during the hearing, and wanted to read from his "manifesto", but was stopped. They also pointed out the contradictions in his statements about working alone and with accomplices.

Breivik was formally charged at the hearing for Friday's twin attacks under terrorism laws, and was remanded in custody for eight weeks, with the first four to be spent in solitary confinement.

The Oslo court decided to hold the hearing in private after online campaigners petitioned for a media blackout.

More than 61,000 people urged the court to be closed through a campaign on Facebook, saying an open hearing would give the gunman a platform.

They wrote: " Do not allow this murderer a world stage to stand on. Close the doors to the hearing on Monday! He wants to have open doors so that the recording can then be shown on TV stations worldwide."

Breivik arrived at the Oslo court on Monday afternoon shortly after a one minute's silence was held across the country for the 93 victims. The hearing ended around 30 minutes later, the AFP news agency reported.

The gunman published a 1,500-page "manifesto" of racist hatred online before carrying out the country's deadliest atrocity since World War II and one of the world's worst shooting rampages in history.

When interrogated earlier, Breivik reportedly said the attacks were "cruel" but "necessary".

If convicted, Breivik's maximum time in jail would be just 21 years. However it is possible under Norwegian law for his sentence to be extended if he is deemed a threat to the public.

Police said they would be conducting an investigation into their response to the twin attacks, after they were criticised for sending a car, not a helicopter, to Utoeya.