Anders Behring Breivik, who has confessed to twin July attacks that killed 77 people in Norway, will see his solitary confinement lifted in theory next week though in practice he will remain isolated, police said on Thursday.

The rightwing extremist has been held in isolation since his arrest on July 22 - something he has described as a form of 'sadistic torture' - amid fears he may contact accomplices and get them to destroy evidence.

Police have since come to the conclusion that the 32-year-old had probably acted alone.

"For every day that passes we are increasingly sure," police prosecutor Christian Hatlo told reporters, adding 'we have found nothing to suggest that accomplices exist even though we refuse to definitively rule out the possibility'.

Police have therefore decided to stop requesting that Oslo's district court grant them extensions of Behring Breivik's solitary confinement, a legal status they have had to apply for every four weeks since his arrest.

"We will not extend the solitary confinement beyond October 17," Hatlo said.

It is rare for solitary confinement to be maintained beyond 12 weeks - a limit Breivik will reach next Monday.

However, his status at the high-security Ila prison will not change in practice, and he will remain fully isolated.

"He will not be allowed to receive mail or visitors and he will have no access to media," Hatlo said.

"He will also be kept apart from other prisoners for his own safety," he said.

According to Norwegian media, a number of prisoners and members of the criminal underworld have vowed to kill Behring Breivik.

Behring Breivik's only contact with the outside world will remain limited to prison guards and the chaplain, police detectives and his lawyer, Geir Lippestad.

Lippestad meanwhile said on Thursday he intended to meet the prison administration to request a softening of his client's conditions.

"At one point or another, he will have to be able to have contact with other people and to benefit from the same conditions as the other prisoners," he told public broadcaster NRK.

"I will therefore ask that he be allowed to meet the other inmates," he said.

Behring Breivik will remain in custody until at least November 14, when a judge is expected to say whether or not to extend his custody further.

He is expected to remain in preventive custody until his trial begins, probably during the first half of next year.

The extremist has admitted setting off a car bomb outside the government offices in Oslo on July 22, killing eight people, before going on a shooting rampage on the nearby island of Utoeya where the ruling Labour Party's youth wing was hosting a summer camp.

Sixty-nine people, mostly teens, died in the shooting massacre and police have said they found 186 empty shell casings strewn around the island.

In a manifesto he published on the Internet just before the attacks, Behring Breivik said he was on a 'crusade' against Islam and professed his hatred for Western-style democracy, saying it had spawned the multicultural society he loathed.

Police said on Thursday that Behring Breivik had claimed there were up to 80 cells in Europe engaged in anti-Islam crusades like his, 'but we don't believe it'.