Germany and Finland say they are “deeply concerned” after an undersea cable linking the countries was severed.
The rupture of the 1,170km (730-mile) telecommunications cable – which is being investigated – comes at a time of heightened tension with Russia.
The two countries’ foreign ministers said in a joint statement: “Our European security is not only under threat from Russia’s war of aggression against Ukraine, but also from hybrid warfare by malicious actors.”
Damage to pipelines in the Baltic Sea has raised fears of sabotage in recent years.
Separately, a 218km (135-mile) internet link between Lithuania and Sweden’s Gotland Island also lost service on Sunday morning, a Swedish telecommunications company said.
In October 2023 a natural gas pipeline between Finland and Estonia was severely damaged. Finnish officials later said the incident had been caused by a Chinese container ship dragging its anchor.
And German prosecutors are still investigating the explosion of Nord Stream gas pipelines between Russia and Germany in 2022.
There have been conspiracy theories around that attack, with unconfirmed rumours that either the Ukrainian, Russian or US government was behind it.
The latest incident involves a C-Lion1 fibreoptic cable linking the Finnish capital, Helsinki and the German city of Rostock, which stopped working around 02:00 GMT on Monday.
Finnish network operator Cinia said all fibre connections in it had been cut.
“These kinds of breaks don’t happen in these waters without an outside impact,” a Cinia spokesperson told local media.
Samuli Bergstrom, a Finnish government cybersecurity expert, said the failure had not affected internet traffic between the two countries as other cable routes were available.
