General Mark Rutte says the military alliance will step up patrols in the Baltic Sea area as Finnish investigators work to establish whether a ship linked to Russia sabotaged undersea cables there this week.

NATO said on Friday it would boost its presence in the Baltic Sea after the suspected sabotage this week of an undersea power cable and four internet lines, while alliance member Estonia launched a naval operation to guard a parallel electricity link.

"We are closely monitoring the investigations conducted by Estonia and Finland and are ready to provide further assistance," Rutte assured after meeting with Estonian Prime Minister Kristen Michal. The meeting focused on the "possible sabotage" of telecommunications cables in the Baltic Sea.