Oslo: The suspect in Norway's twin attacks that killed at least 93 people and wounded nearly 100 more claims he acted alone, police said on Sunday as a raid on an Oslo flat failed to find any link to the attacks.

Prime Minister Jens Stoltenberg and Norway's King Harald V and Queen Sonja led the nation in mourning at an emotional memorial mass in Oslo Cathedral for the victims of Friday's twin bomb and gun attack.

Stoltenberg said in an address to the hundreds of mourners that the names and photographs of those who were killed would soon be released and "the scale of the evil will then emerge."

The death toll rose to 93, after one of those wounded in the attacks died in hospital.

At least seven people were killed in a car bomb blast outside government buildings in Oslo and a further 85 were shot dead on the nearby island of Utoeya, where a Labour party youth meeting was being held.

Police said they detained several people in a swoop on an Oslo property thought to be connected to the attacks, but released them shortly afterwards.

"No explosives were found at the location and those detained have been released," Oslo police said in a statement following the raid in the Sletteloekka district of the capital.

"Police have nothing that could enable these people to be connected with acts of terror."

Neighbours in the area told AFP that police had detained six people around midday. Norwegian television showed images of the operation centred on a large shed near a parking lot.

The man arrested at the end of Friday's shooting rampage, named as 32-year-old Anders Behring Breivik, acknowledged the facts resulting from his actions, but rejected "criminal responsibility," according to police.

His lawyer, Geir Lippestad, told Norwegian television his client was comfortable with what he had done.

"In his mind, he has the feeling that there was nothing reprehensible in what he has done," Lippestad told NRK.

At the emotion-filled service in Oslo, Stoltenberg wiped his face with a handkerchief and told the hushed congregation that despite the tragedy Norway would demonstrate "more democracy, more openness, more humanity, but without naivety."

"We are a small country but we are a proud people," he said as a woman in the congregation sobbed uncontrollably, adding that Norway "will never abandon its values."

The leader of the Labour Party's youth group, Eskil Pedersen, wept openly during the service.

"We are gathered under the signs of mourning and of hope," the bishop of Oslo, Ole Christian Kvarme, told the congregation, many of them wearing black.

Hundreds of people had gathered earlier outside the cathedral where a shrine has been set up amid a sea of flowers laid in tribute to the victims.

Stoltenberg and Pedersen each laid a white rose near the improvised shrine before the service began.

Investigators were today poring over a rambling 1,500-page tract that emerged on the Internet apparently written by Behring Breivik, in which he said he had been preparing the "martyrdom operation" since at least autumn 2009.

Police were still trying to establish whether there was "one or several" people involved in the shooting attack.

"During questioning, he said he acted alone," police commissioner Sveinung Sponheim said earlier. "We will try to verify this through our inquiry." Some witness accounts said a second gunman had taken part.

Behring Breivik, 32, was arrested on Friday, and was "cooperative" according to police on Sunday.

"He feels that it was cruel to have to carry out these acts but that, in his head, it was necessary," Lippestad said.     The Internet document, part diary, part bomb-making manual and part political rant in which he details his Islamophobia, explains how he set up front mining and farming businesses to prepare the attacks for which he was arrested on Friday.

"The reasoning for this decision is to create a credible cover in case I am arrested in regards to the purchase and smuggling of explosives or components to explosives fertiliser," says the tract. It was unclear on Sunday when the document had been put on the Internet.

As harrowing testimony emerged from the summer camp where scores of youngsters were mown down, Norway was struggling to understand how a country famed as a beacon of peace could experience such bloodshed on its soil.

"Many of those who have died were friends," Stoltenberg said. "I know their parents and it happened at a place where I spent a long time as a young person... It was a paradise of my youth that has now been turned into hell."

The toll could rise further as the search continued for four or five people still missing from the island, aided by a mini-submarine and Red Cross scuba divers.

Blond-haired Behring Breivik described himself on his Facebook page as "conservative", "Christian", and interested in hunting and computer games like World of Warcraft and Modern Warfare 2, reports said.

He also described himself as director of Breivik Geofarm, an organic farm that may have given him access to chemicals used in the production of explosives.

Police spokesman Roger Andersen described the suspect as a "Christian fundamentalist", adding that his political opinions leaned "to the right".

The head of the populist right-wing Progress Party (FrP), Norway's second-biggest political party, confirmed Behring Breivik had been a member between 1999 and 2006 and for several years a leader in its youth movement.

Anti-fascist monitors meanwhile said Behring Breivik was also a member of a Swedish neo-Nazi Internet forum named Nordisk.