Anders Breivik, in his first court appearance since the attacks on Friday, said his shooting rampage, which killed 76 people, was aimed at saving Europe from a Muslim takeover and revealed that there were “two further cells” in his terror organisation.
He had previously said he was acting alone and police currently have no other suspects.
The judge said the claim would be investigated and in a press conference police officers said they “cannot completely rule out that someone else was involved”.
Wearing a red jumper, after being refused permission to wear a black uniform, the 32-year-old killer admitted responsibility for the attacks but denied he was guilty of any criminal charges.
He claimed he had not been trying to kill as many people as possible but instead wanted to send out a “sharp signal to the people” and to “stop the takeover by Muslims and Marxists”.
Breivik, who was driven to the Oslo hearing in an armoured police convoy, was met by a huge crowd of people outside the courthouse who jeered as the cavalcade arrived.
Some tried to bang the cars in anger and screamed “coward”, “traitor” and “racist”. Police eventually bundled Breivik into the building through an underground tunnel, avoiding the full wrath of the crowd.
He was taken to court 828, on the eighth floor of the building, which was closed to the public to avoid giving Breivik a platform for his views. The hearing lasted 35 minutes.
During the hearing Breivik, who appeared calm and restrained, began reading from his manifesto, but was stopped after two minutes.
Police attorney Christian Hatlo said the so-called document was more than 1500 pages long and Breivik appeared to be told it would take too long to read out and was irrelevant to the proceedings.
A similar document boasted of 80 “solo martyr cells” in western Europe that aimed to overturn governments that tolerated Islam.
The court ruled that Breivik be held in solitary confinement after he boasted of carrying out the massacre to “save Norway”.
Prime Minister David Cameron yesterday said Britain was taking “extremely seriously” claims Breivik had links with far-right groups in the UK.
Judge Kim Heger said Breivik had been charged with terrorism following Friday’s attacks and ordered he be held in custody for eight weeks because there was a risk he might “tamper with evidence” if released. He will be banned from seeing visitors, receiving letters, reading newspapers or watching TV during his incarceration.
In a televised statement, Judge Heger said: “The accused believes that he needed to carry out this act in order to save Norway and western Europe from, among other things, cultural Marxism and Muslim takeover.”
Quoting Breivik, the judge added: “The operation was not to kill as many people as possible but to give a strong signal … that, as long as the Labour Party keeps on its ideological line and keeps deconstructing Norwegian culture and mass importing of Muslims, then they must assume responsibility for this treason. Any person with a conscience cannot allow his country to be colonised by Muslims.”
Breivik left the court approximately 30 minutes after arriving, speeding off in a small convoy of two black SUVs led by police motorcyclists.
Meanwhile, Breivik’s father said he was ashamed and disgusted by his son’s acts and wished he had committed suicide.
“I don’t feel like his father,” said former diplomat Jens David Breivik from his secluded home in southern France. “How could he just stand there and kill so many innocent people and just seem to think that what he did was OK? He should have taken his own life too. That’s what he should have done.”
Breivik said he first learned the news of his son’s attacks from media websites. “I couldn’t believe my eyes. It was totally paralysing and I couldn’t really understand it.”
“I will have to live with this shame for the rest of my life. People will always link me with him,” he said.
Jens David Breivik said he had severed all contact with his son in 1995 when the latter was 16.
Police surrounded his house in the south of France. Initially they were searching the premises, but later said they were there to ensure public order.
Police have now revised the Utoya island killings from 86 to 68 but increased the bomb death toll by one to eight.
The overall toll in the attack now stands at 76 instead of 93 – still one of the worst modern mass murders in peacetime.
It further emerged that Breivik had been on an intelligence watchlist since March.
Norway’s national security service PST confirmed that Breivik had been put on the list after illegally paying 120 kroner (£17) for chemicals online from a Polish retailer.
It is understood the Norwegian intelligence service had not acted on the information because they did not believe it was “relevant”.