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He cited recent attacks on undersea cables in the Baltic Sea, cyber attacks on European public transport, and unidentified drones spotted over German power stations and other infrastructure.

It follows reports of damage to a major undersea cable in the Baltic Sea.

A record-breaking tunnel is being built under the Baltic Sea between Denmark and Germany, which will slash travel times and improve Scandinavia's links with the rest of Europe.

And a breakdown can affect just about everywhere: If Africa or the Baltic Sea or the Philippines were to become isolated, the repercussions would be felt all over the globe.

"The Baltic Sea has become the Nato Sea," he notes.