Alleged sabotage of undersea cables in the Baltic Sea has heightened tensions in NATO’s northern theater, prompting allied leaders to boost surveillance and military presence.

NATO chief Mark Rutte condemned the attacks on critical infrastructure, citing recent incidents like the Christmas Day damage to Estonia’s Estlink 2 power cable and internet cables.

Finnish authorities linked the suspected sabotage to the Eagle S, a ship reportedly part of Russia’s “shadow fleet,” which evades sanctions using aging vessels under opaque ownership, ABC News has reported.

Investigations are ongoing, as experts estimate up to 1,400 ships in this shadow fleet, some potentially doubling as saboteur vessels.

Written by B.C. Begley