Finland has seized an oil tanker suspected of having severed undersea power and internet cables, with Finnish authorities saying the vessel may have been part of Russia's "shadow fleet" of ships aimed at skirting Western sanctions.

Finnish police said on Thursday they are investigating whether a foreign ship was involved in the damage of an undersea power cable connecting Finland and Estonia following a sudden outage on Wednesday.

Finnish authorities on Thursday seized a ship carrying Russian oil in the Baltic Sea on suspicion it caused the outage of an undersea power cable connecting Finland and Estonia a day earlier, and that it also damaged or broke four internet lines.