Armed Norwegian police staged an action in Oslo on Sunday linked to Friday's shootings and bombing that killed at least 92 people, a police lawyer said.

"The operation is related to the bomb attack in Oslo," he told Reuters, confirming an online report in Verdens Gang newspaper. Sources said the police counter-terrorism force, known as Delta, was involved in the operation.

Police have previously said that they were likely to stage follow-up actions as they try to confirm that there are no additional threats. Police declined comment on whether there were any arrests.

 A right-wing zealot who admitted to bomb and gun attacks in Norway that killed 92 people on Friday claims he acted alone, Norway's police said on Sunday.

"He has admitted to the facts of both the bombing and the shooting, although he's not admitting criminal guilt," acting police chief Sveinung Sponheim told a news conference about detained suspect Anders Behring Breivik.

"He says that he was alone but the police must verify everything that he said. Some of the witness statements from the island (shootings) have made us unsure of whether there was one or more shooters."

Sponheim said police had no other suspects for the worst massacre committed in Norway since World War Two, in which 97 people were also wounded. Several people also remain missing, which could raise the death toll.

Reuters