IMO how you put it is perhaps a bit misleading -
You should probably point out that it was the left wing surveilling each other. More specifically it was the Socialist Labour party (AP) which conducted surveillance of the communist AKP-ML (and NKP) for the reason of being in control of the left-wing agenda in Norway.
Considering that AKP-ML was part of the stay-behind groups, known as "Gladio" (something that ironically (?) sprung out of NATO [0]), armed and trained PLO and marxist revolutionaries in Israel, and had networking with other similar ideological extreme radical left groups such as Red Army Fraction (Germany, Japan, Italy), Black Panthers and Weather Underground in the US, as well as IRA in Ireland and close ties with Pol Pot[1] and other groups in Asia. And they were actually planning armed revolution in Norway - the surveillance was called for (ref. Willoch). However, the labour party's close ties with the IC and media in Norway was peculiar (at the time there were only a single national government owned TV/radio broadcaster, NRK, rooted in the labour party) and these three "fractions" held meetings frequently.
> No secret prisons
Partly correct - in Norway some people were thrown into mental hospitals instead. A famous case would the Kaare Torvholm [2] case which got arrested, together with the sheriff and a deputy (the equivalent of) and sent to mental institution which lead a local newspaper to raise the question if a "schizophrenic epidemic" had reached the shores (later picked up by VG, a national newspaper). This for reporting discrepancies with money (pension funds and more) in the fishing industry which was used as part of intelligence networks (at the time).
As the original thread topic:
Norwegian military has been conducting surveillance for a long time, illegally and including Norwegian citizens. The process right now is to push through laws which allows for this sort of surveillance (and let them keep the data they have, which is already shared with US and UK). These laws will just "harmonize" the Norwegian laws to those of the UK and partly US. These operations centers are located several places, not just in this region, but from the west of Norway (Haakonsvern) to Troms in the north (Setermoen) and involves what is called "svarte operasjoner" ("black ops" in English). One of these operations got public attention some years ago when it was revealed that they were spying on the King's email traffic [3].
[0]: https://en.wikipedia.org/wiki/Operation_Gladio
[1]: https://cambodiatokampuchea.wordpress.com/2015/08/30/norwegi...
[2]: https://www.fiskersiden.no/forum/index.php?/topic/22444-fisk...
[2]: http://detsomstatennorgeskjuler.origo.no/-/bulletin/show/548...
[3]: https://www.vg.no/nyheter/innenriks/forsvaret/forsvaret-bekl...