Norway's security service PST says extreme Islamism remains the biggest terror threat in Norway but also says threats from lone-wolf types have increased following the July massacre that left 77 people dead.

According to the Associated Press, PST said Tuesday, January 17 the level of activity among extreme Islamist networks in Norway is high and that homegrown extremism is on the rise.

It said threats from organized far-right groups remains low, but that "concrete threats and general manifestations of threats from solitary individuals, irrespective of ideological motivation, have increased."

It also warned that actions such as Anders Behring Breivik's deadly attack in July could inspire others to attempt similar attacks.

The 32-year-old has confessed to a bomb-and-shooting spree on July 22 that killed 77 people.