At a time when the eight NATO nations bordering the Baltic Sea are on high alert after a string of undersea power and internet cables were suspiciously severed, Russia's shadow fleet is getting extra attention.

NATO is ratcheting up its guard against suspected attempts to sabotage underwater energy and data cables and pipelines that crisscross the Baltic Sea.

Estonia's navy is prepared to act against vessels that pose a danger to Baltic Sea infrastructure even if they are in international waters, a senior official patrolling the busy Gulf of Finland shipping lane said on Thursday.

Northern Europe’s Baltic Sea is bordered by nations including Germany, Russia and Latvia. Many critical cables and pipelines cross the seafloor. But with tensions rising in the region, NATO is looking for ways to ensure all that infrastructure stays safe.

Under steel grey skies, the Dutch minehunting vessel Schiedam cuts through the waters dividing Denmark and Sweden, part of NATO's Baltic Sentry mission to protect underwater infrastructure in the Baltic Sea.