Prosecutor Paal-Fredrik Hjort Kraby says the names of other Britons came up when police questioned British anti-Muslim blogger Paul Ray last week. Investigators say they haven't yet found any evidence that Breivik had any accomplices, but don't rule out the possibility.
The British citizens will be questioned shortly in Norway or in Britain, Hjort Kraby said on Thursday.
Breivik was questioned again on Wednesday about the Oslo bombing and shooting spree on July 22 in which he killed 77 people.
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The questioning was focused on Breivik's anti-immigration manifesto, his alleged links to a group called the Knights Templar and potential ties to Britain, Hjort Kraby said.
Breivik claims he carried out the attacks as part of a network of modern-day crusaders - the Knights Templar - to launch a revolution against a Europe spoiled by Muslim immigration, and that there are other cells ready to strike.
Ray, an Englishman who writes an anti-Muslim blog, has said he was one of the founders of the Knights Templar, but claims he doesn't know Breivik and is not the mentor cited in the Norwegian's rambling manifesto.
After being questioned by police last week, he said he had been "completely honest and open with the police ... and they know I don't have anything to do with this".
This week police have also searched the farm where Breivik built the bomb he used in the attack and confiscated some 1000 objects, Hjort Kraby said.
He said police are considering bringing Breivik back to the farm for more detailed questioning about how he constructed the bomb, but haven't made any such decision yet.
