Norway has blamed Russia for a cyber-attack on the email system in the Norwegian parliament in August.
Foreign Minister Ine Eriksen Soreide called it a serious incident affecting the country’s “most important democratic institution.”
“Based on the information available to the government it is our assessment that Russia stood behind this activity” she said without giving any evidence.
Moscow has rejected the claim, calling it a “serious and wilful provocation.”
Ms Soreide said in a statement that Norway’s security and intelligence services were “co-operating closely to deal with this matter at the national level.”
In response, Russia’s embassy in Oslo hit back at the “unacceptable” announcement, saying no evidence had been presented.
“Millions of cyber attacks are annually committed from abroad against Russian state internet resources… but this does not give us the right to indiscriminately blame authorities of the countries of their possible origin,” the embassy added.
In September, Norwegian authorities said that email accounts belonging to several officials had been compromised during a cyber-attack, and some information had been downloaded. But the full extent of damage caused by the hack has not been made public.
Norway’s allegation comes during a time of increasingly strained relations with Russia. Both countries share an Arctic border, and Norway is a member of Nato.