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.

Police and media reports say that Finnish authorities have detained a Russia-linked ship as they investigate whether it damaged a Baltic Sea power cable and several data cables.

An unplanned break in service on the Estlink 2 interconnector occurred at 1026 GMT, operator Fingrid said in a statement on the Nordpool

The Estlink 2, an undersea power cable linking Finland and Estonia, was seriously damaged on Christmas Day. Authorities are investigating the incident as a possible act of sabotage.

Finland’s prime minister says authorities are investigating an interruption in a power cable under the Baltic Sea between his country and Estonia.

The Eagle S is flagged in the Cook Islands but was described by Finnish customs officials as a suspected part of Russia’s so-called shadow fleet.

Damage to the power cable in the Baltic Sea is the latest in a spate of murky disruptions to undersea cables that have put European authorities on high alert.

A vessel delivering oil for Russia was detained by Finland authorities on Thursday in connection with an undersea cable cutting incident that disconnected electricity to Estonia.

NATO Secretary-General Mark Rutte said Friday that the military alliance will step up patrols in the Baltic Sea region as Finnish investigators work to establish whether a ship linked to Russia sabotaged undersea cables there this week.

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.