The director of the Norwegian Police Security Service Beate Gangås warned cyber attacks are increasingly being carried out against European countries to stoke fear and unrest.
During the April incident, hackers gained access to a digital system which remotely controls one of the dam's valves and opened it to increase the water flow, NRK said.
The valve was open for about four hours but did not pose a danger to the surrounding area, NRK reported.
A three-minute long video showing the dam's control panel and a mark identifying a pro-Russian cybercriminal group was published on Telegram in April, police lawyer Terje Nedrebø Michelsen told NRK.
Similar videos have previously circulated on social media but the announcement by Norwegian police marked the first time since 2022 that officials have publicly suggested that pro-Russian hackers may have successfully targeted critical water infrastructure in Europe.
Gangås told NRK that state actors typically use other groups to hack into facilities to show "look what we can do if we want to," before bragging about it afterwards.
She spoke on Wednesday alongside the head of Norway's intelligence agency at a briefing titled: "Hybrid attacks against Norway: are we at war?".
NRK said Gangås warned such activity is only likely to increase in Norway and other European countries.
The Russian embassy in Oslo said Gangås' declarations were "unfounded and politically motivated".
"It is obvious that the PST is unsuccessfully trying to substantiate the mythical threat of Russian sabotage against Norwegian infrastructure this year, which it itself invented in its February (annual) report," it said in an emailed statement to Reuters.
After her speech, Gangås told Reuters that she was going public with the attribution to warn the general population and to try to prevent Russia from launching further attacks.
"I want Norwegians to be prepared," she said in an interview.
NATO-member Norway shares a border with Russia in the Arctic.
with Reuters
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