The following day the Finnish authorities seized the Eagle S, a Cook Islands-flagged tanker carrying Russian oil, on suspicion of deliberately damaging the Finnish-Estonian Estlink 2 power line and four telecoms cables by dragging its anchor across the seabed.

"Both of Elisa's cables have now been repaired," a spokesperson for the Finnish telecoms group said on Monday, adding that both lines had been cut.

The Eagle S vessel was brought to a bay near the Finnish port of Porvoo, where police are currently collecting evidence and questioning the crew.

Repairing the Estlink 2 power cable is expected to take some seven months, operators Fingrid of Finland and Elering of Estonia have said.