Norway's domestic security agency has said that Russian hackers linked to the country's military intelligence service were "likely" behind a cyber attack against the Norwegian parliament this year.
The network operation behind the attack was part of "a broader national and international campaign that lasts at least since 2019" the Norwegian Police Security Service (PST) said in a statement.
"The analyses show that it is likely that the operation was carried out by the cyber actor referred to ... as APT28 and Fancy Bear," the PST added, explaining that the "actor" was linked to Russia's military intelligence service.
But the Norwegian agency said they closed the case due to a lack of sufficient evidence.
On 1 September, the country's parliament (Storting) announced that it had been the target of a "vast" computer attack a few days earlier.
The attack had affected the Storting's email system of politicians and employees, which contains information "of great interest to several foreign states' intelligence services".
The PST said on Tuesday the breach had used "brute force" to crack users' passwords through trial and error and had downloaded "sensitive" information.
The attackers also tried "to move further into the Storting's computer systems" without success.
The investigation also confirmed vulnerabilities within the Storting, such as insecure passwords, and stated that common security mechanisms and settings would prevent future hacking.
The origin of the attack was not detailed at the time, but in October, Foreign Minister Ine Eriksen Søreide accused Russia of being behind it.
The Russian embassy in Norway stated that the accusations were "unacceptable" and a "serious, deliberate provocation, destructive to bilateral relations."
The recent allegations of espionage have tarnished relations between Russia and its NATO neighbour, but Moscow has repeatedly denied involvement in hacking attacks.
Earlier this year, both countries expelled a diplomat after a Norwegian citizen was arrested in an Oslo restaurant on accusations of industrial spying for Russia.