NATO is ready to help Finland and Estonia as Finnish authorities probe an oil tanker that sailed from a Russian port over the possible "sabotage" of a power cable linking the two member countries, alliance chief Mark Rutte has said.

"Spoke with (Estonian Prime Minister) Kristen Michal about reported possible sabotage of Baltic Sea cables. NATO stands in solidarity with Allies and condemns any attacks on critical infrastructure.

"We are following investigations by Estonia and Finland, and we stand ready to provide further support," Mr Rutte said on X.

Earlier, Finnish authorities said they were investigating an oil tanker that sailed from a Russian port for the "sabotage" of a power cable linking Finland and Estonia that was damaged the previous day.

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

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

"According to our understanding an anchor of the vessel that is under investigation has caused the damage," he added.