Norway has expelled 15 Russian officials that it had accused of spying under diplomatic cover.
Foreign minister Anniken Huitfeldt said Norway would not allow Moscow to use its embassy to carry out “covert intelligence activities”.
It is the latest in a string of Russian expulsions since it launched the full-scale invasion of Ukraine last year.
The Kremlin will respond and is weighing up an “appropriate answer”, Russian news agency Tass reported.
Norwegian authorities had monitored the individuals “over time” before they were declared persona non grata – unacceptable or unwelcome – a government statement said.
They must leave the country “shortly”, but further details about their alleged activities have not been revealed.
Norway said Russia poses the “greatest intelligence threat” the country faces, and that the threat is increasing against the backdrop of Europe’s “deteriorating security situation”.
Norway shares a 197km (122-mile) land border with Russia in the Arctic, and their relations have suffered throughout the Ukraine crisis.
Despite not being a member of the European Union, Norway has emulated several European sanctions against Russia.
It expelled three individuals it said were intelligence officers in April 2022, a move which Russia responded to by expelling three Norwegian diplomats.
In October 2022, Norwegian police arrested a university lecturer accused of spying for Moscow.
The academic, identified in Norwegian media as Russian national Mikhail Valerievich Mikushin, had allegedly been posing as a Brazilian. He has denied the charges against him.
Announcing the latest expulsion, Norway’s foreign minister stressed that the government wants to maintain normal diplomatic relations with Moscow.
“But we will not accept that diplomatic missions are misused for the purposes of carrying out covert intelligence activities,” Ms Huitfeldt added.
Dozens of Russian officials accused of abusing diplomatic privileges to carry out intelligence work have been ordered to leave European countries in recent months, including by Ireland, the Netherlands, Austria, the Czech Republic and Belgium.