Finnish investigators probing the damage to a Baltic Sea power cable and several data cables said they found an anchor drag mark on the seabed, apparently from a Russia-linked vessel that has already been seized.

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.

Finnish police have discovered traces on the bottom of the Baltic Sea stretching for dozens of kilometers. It is believed that a tanker, which was carrying Russian oil, severed a power line and four telecommunications cables with its anchor,