(CNN) Norwegian authorities have arrested a high-profile American white supremacist, hours before he was due to give a speech at a far-right conference in Oslo on Saturday.

The detained American, Greg Johnson, is editor-in-chief of the white nationalist Counter-Currents Publishing group.

He had been scheduled to speak at the Scandza Forum, a network known for its anti-Semitic and racist views.

Norway's intelligence service considered Johnson "to be a threat, not because of what he could do but because of his hate speech and his previously expressed support for Anders Breivik ," spokesman Martin Bernsen told CNN.

Right-wing terrorist Breivik killed 77 people -- dozens of them teenagers -- in a bombing in Oslo and a mass shooting at a youth camp on nearby Utoya Island in July 2011.

Johnson was arrested under the country's immigration act and Norwegian authorities are now working "as quickly as possible to get him out of the country," said Bernsen.

He could be deported within a matter of hours, Bernsen said, adding: "We have no interest in keeping him here."

On its website, Counter-Currents Publishing confirmed Johnson's arrest. But Johnson has refuted the accusations against him, saying he has "never supported Breivik's crimes."

"I have always consistently condemned violence and terrorism," Johnson wrote on the Counter Currents Publishing site. "In fact, I do not know of anyone else who has so clearly and unequivocally spoken against right-wing terrorism as me."

Johnson was still in Oslo on Sunday; he is understood to have hired a lawyer to try and secure his release.

Norway has been the target of several far-right terror attacks in recent years.

In 2011, Breivik unleashed the deadliest attack on the country since World War II. He was later sentenced to 21 years in prison -- the maximum possible sentence.

Earlier this year Norway's intelligence service reported that right-wing terrorism was on the rise globally, and warned that it was likely the country would be targeted in the near future.

Bernsen said Johnson's arrest, and similar actions "are part of how we prevent attacks, such as the one we saw in New Zealand, from happening here as well."