The government said it would summon the Russian ambassador over the matter, Defence Minister Troels Lund Poulsen told a press conference.

Water pipes were exploded in the 2024 attack conducted by Z-Pentest, in which household water supply was affected, he said.

On the eve of Denmark's municipal and regional elections in November, the websites of several political parties, municipalities, public institutions and a defence company were inaccessible due to a cyberattack claimed by the Russian hacker group NoName057.

"We are very confident that these are pro-Russian groups linked to the Russian state," said the head of Denmark's military intelligence agency (FE), Thomas Ahrenkiel.

"We have taken numerous initiatives and we will take more, because Russia's way of acting is profoundly unacceptable," Lund Poulsen said.

The government said it intended to set up a new cyber-surveillance network and an online operations centre, among other things.

"It's very serious to be able to attribute the attacks to the Russian state. That it's not just sympathisers, but a group directly linked to the Russian state. This underscores that the situation is particularly grave," Minister for Resilience and Preparedness, Torsten Schack Pedersen, told public broadcaster DR.

"We are not in a state of war, we are not in a state of peace, but we are in hybrid warfare," he said.