Fifteen Russian diplomats expelled by Norway this week had sought to recruit sources, intercept communications and buy advanced technology, the Norwegian PST security police said on Friday.
The diplomats' real employers were the Russian GRU, FSB and SVR intelligence services, PST counterintelligence chief Inger Haugland told a news conference.
"This lowers the threat from Russian intelligence in Norway by permanently reducing the number of intelligence officers operating under diplomatic cover," Haugland said of the expulsions.
The move is Norway's largest expulsion of Russian diplomats and is the latest in a series of expulsions by Western nations since the start of Moscow's full-scale invasion of Ukraine.
Norway's action will remove more than one third of around 40 Russian diplomats in Norway, according to the Norwegian foreign ministry.
The expelled diplomats, all men, worked at the consular, trade and embassy sections of the Russian delegation in Oslo, PST Superintendent Dag Roehjell told Reuters.
One of them tried to buy advanced, subsea technology on behalf of Russia's GRU military intelligence agency, Haugland said.
Russian intelligence is particularly interested in the Norwegian defence sector, including what it contributes in military support to Ukraine, and its oil and gas sector, given that it is now Europe's biggest gas supplier, Roehjell said.
He said Norway's oil and gas technology was coveted by Moscow given it cannot access such technology due to international sanctions and now tries to get it by spying.
NATO-member Norway shares a border with Russia in the Arctic. It has stepped up security since the start of the Ukraine war, especially around its oil and gas installations.
Russia on Friday said relations with Norway had been dealt "a serious blow" and the Nordic country was "increasingly confirming the status of a state hostile to Russia".
"These actions will not go unanswered on our part, we will implement a tough response," Foreign Ministry spokeswoman Maria Zakharova said in a statement, without giving specifics.
In October, Norway arrested a suspected Russian spy it described as an illegal agent - an intelligence operative without official government links who assumes a covert persona.
Norway has also investigated a number of drone sightings around oil and gas infrastructure onshore and offshore in the wake of explosions last year on the Nord Stream pipelines.
(Reporting by Gwladys FoucheEditing by Terje Solsvik, Peter Graff and Nick Macfie)
