"This transfer is mainly due to construction inside the prison and to planning needs among the personnel," said Knut Bjarkeid, the warden of Ila prison near Oslo where Breivik has largely been held since his arrest on July 22nd shortly after carrying out his twin attacks.
"We have asked for a break," he said, noting that occasionally moving high-profile inmates to other prisons can be beneficial to policy development.
How long the 33-year-old right-wing extremist would stay at the Skien prison, some 130 kilometres south-east of Oslo, remained unclear, he said.
Norway on Sunday marked the one-year anniversary of the July 22nd 2011 attacks.
On that day, Breivik first bombed a government building in Oslo, killing eight people, before going on a more than hour-long shooting rampage on the nearby island of Utøya, where the ruling Labour Party's youth wing was hosting a summer camp.
He killed 69 people on the island, most of them teenagers.
Breivik's 10-week trial ended on June 22nd, and his verdict is expected on August 24th
Regardless of whether he is found criminally sane and sentenced to prison or criminally insane and sent to a closed psychiatric ward, Breivik is likely to be mainly held at Ila.
The high-security prison has already converted one wing so it can be used as a miniature hospital.
The killer will in any case be held apart from the other inmates and should benefit from a number of measures to ease his isolation.
Last May, Bjarkeid told Norwegian media the prison was for instance looking into the possibility of hiring people to play sports and chess with Breivik.