German Defence Minister Boris Pistorius has said that damage done to two underwater data transmission cables running between Germany and Finland was deliberate.

“No one believes that these cables were accidentally cut,” Pistorius said in remarks made on the sidelines of a meeting of EU defence ministers in Brussels.

“We also have to assume, without knowing it yet, that it is sabotage,” he declared, adding that neither Germany nor Finland yet knows who was responsible for damage.

Germany and Finland announced on Monday that they had discovered a severed fibre-optic undersea data cable between the two countries, and that an investigation into the incident is underway.

In a joint statement, they said they did not know who was responsible for the damage, but that the incident came at a time when “our European security is not only under threat from Russia‘s war of aggression against Ukraine, but also from hybrid warfare by malicious actors”.

Pistorius also pointed to so-called “hybrid actors” as being potentially responsible for the damage.

“We have to state, without knowing specifically who it came from, that it is a ‘hybrid’ action” Pistorius said — implying that Russia, often considered responsible for acts of “hybrid warfare”, could be at least in part to blame for the incident.

“It’s clear that we have to have more protection to critical infrastructure” Finland’s Defence Minister, Antti Häkkänen, said at the same meeting in Brussels.

“The fact that such an incident immediately raises suspicions of intentional damage speaks volumes about the volatility of our times,” the two countries said in their joint statement.

Finnish state-controlled data services provider Cinia said the damage to the data cable, which runs almost 1,2000 kilometres from the Finnish capital Helsinki to the German port of Rostock, was detected on Monday.

The incident is not the first to involve damage to underwater infrastructure in the Baltic Sea. On Sunday morning, a 218-kilometre internet link running between Lithuania and Swedish island of Gotland also lost service, according to a Swedish telecommunications company.

In 2022, Nord Stream gas pipelines under the Baltic Sea exploded, leading to several conspiracy theories around who could be responsible for the attack. Unconfirmed rumours have variously said that the US, Ukraine and Russia could have all played a role.