The suspect, who claimed responsibility for Friday's bomb and gun attacks in Norway that killed 93 people and wounded 97, said he had acted alone, police said Sunday while investigation was still underway.

Despite claim from the 32-year-old suspect Anders Behring Breivik that he acted alone in the twin attacks, "the police must verify everything he said," acting police chief Sveinung Sponheim said at a press conference Sunday morning.

"Some of the witness statements from the island (shootings) have made us unsure of whether there was one or more shooters," added the officer.

The suspect, however, rejected criminal responsibility, said the police.

"He has admitted to the facts of both the bombing and the shooting, although he's not admitting criminal guilt," Sponheim said.

In the latest development, Norwegian police have freed a number of people who were briefly detained in an operation on Sunday prompted by Friday's deadly attacks.

Those detained in the Sunday raid have been released because no evidence prove that they are linked with "acts of terror," Oslo police said in a statement.

The police also said no explosives were found at the location during the operation in the Sletteloekka district, east of the capital.

Earlier reports said six people had been arrested in the police raid on Sunday "linked to the terror investigation," as police spokesman Anders Fridenberg called it.

Meanwhile according to a NRK report, the death toll has risen to 93 after a wounded in the shooting spree died in hospital.

A total of 97 people were wounded in Friday's attacks and several people were still missing, according to local police.

The search team continued their mission for the several still missing, said the police.