With its powerful camera, the French Navy surveillance plane scouring the Baltic Sea zoomed in on a cargo ship plowing the waters below — closer, closer and closer still until the camera operator could make out details on the vessel's front deck and smoke pouring from its chimney.

The Nordic country has opened an investigation into the damage, just weeks after NATO stepped up its military presence in the area following a series of similar incidents.

President of Finland, Alexander Stubb, admitted that there is no certainty about who is responsible for cutting cables in the Baltic Sea. Local media suggest that the authorities may be covering up Russia's involvement.

The NATO alliance is ratcheting up its guard against suspected attempts to sabotage underwater energy and data cables and pipelines that crisscross the Baltic, prompted by a growing catalogue of incidents that have damaged them.