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.

The Cook Islands-registered ship, named by authorities as the Eagle S, was boarded by a Finnish coast guard crew that took command and sailed the vessel to Finnish waters, a coast guard official said at a press conference.

"From our side, we are investigating grave sabotage," said Robin Lardot, director of the Finnish National Bureau of Investigation.