Norway on Thursday announced the expulsion of 15 "intelligence officers" working at the Russian embassy in Oslo, as the embassy condemned the decision, promising a "response."
"The 15 intelligence officers have been engaging in activities that are not compatible with their diplomatic status," Foreign Minister Anniken Huitfeldt said in a statement.
According to the statement the "officers" had been declared "personae non gratae," and must leave "shortly."
Speaking at a press conference Huitfeldt said their activities had been monitored "over time" but she declined to elaborate on what activities had spurred the decision.
"The reaction is strongly negative," Russian embassy spokesman Timur Chekanov told AFP in an email.
"This is another extremely unfriendly step, which will be followed with a response measure," he added.
The foreign ministry said that the decision had been made in response to a "changed security situation in Europe, which has led to an increased intelligence threat from Russia."
Norwegian intelligence services regularly point to Russia and China as the main espionage threats to the country, which is a member of NATO and shares a 198-kilometre (123-mile) border with Russia in the Arctic.
In April 2022, a few weeks after the start of the Russian invasion of Ukraine, Oslo, like several other European capitals, expelled three Russian diplomats suspected of espionage, which led Moscow to retaliate with the expulsion of three Norwegian diplomats.
The two countries, which have long had close ties, especially in the far north, have seen their relations deteriorate considerably as a result of the conflict in Ukraine.
Although it is not a member of the European Union, Norway has adopted almost all the sanctions imposed on Russia by Brussels.
Despite the new expulsion Huitfeldt stressed that "Norway is seeking to maintain normal diplomatic relations with Russia, and Russian diplomats are welcome in Norway."