The 150-kilometer electricity connection EstLink 2 cable was the first to be reported broken. The Finnish Border Guard said it had been "cut."

The outage was reported at 12:26 p.m. on Christmas Day (December 25) by electricity transmission system operators Elering and Fingrid. The damage is roughly in the middle of the gulf, approximately 80 km from the Estonian shore and 70 km from the Finnish coast.

As the broken cable is in Finnish waters, the Finns are leading the investigation with cooperation from Estonia.

On December 26, the Finnish National Bureau of Investigation said the Russian shadow fleet's oil tanker Eagle S – sailing under a Cook Islands flag – likely caused the damage. The tanker is missing an anchor. 

The Border Guard took control of the vessel and detained it in Finnish waters. The agency said the damage to EstLink 2 is being investigated as aggravated vandalism.

The ship's crew was made up of Georgian and Indian citizens, the National Criminal Police said. On December 28 it was moved to a port.

The oil tanker was, according to MarineTraffic, on its way from St Petersburg to Egypt, Finland's public broadcaster Yle reported.

Four other cables connecting Finland to Estonia and Germany were also damaged. Three were linked to Estonia, the Ministry of Economic Affairs and Communications said.

It is not yet known whether there is a connection between the data cables and the EstLink 2 power outage, Yle reported.

On December 27, NATO said it would increase its presence in the Baltic Sea after the incident.

On the same day, Finnish President Alexander Stubb said it is too early to conclude if the cable damage could be attributed to Russian hybrid interference. He told the media there has not been any diplomatic reaction from Russia yet.

EstLink 2 is the latest cable to be damaged in the Baltic Sea by vessels suspected to be linked to China or Russia. In November, cables between Finland and Germany and Sweden and Lithuania were broken.

In October 2023, a gas pipeline connecting Estonia and Finland was damaged by a Hong Kong-flagged ship's anchor.

The latest damage comes after 12 countries agreed to place additional restrictions on Russia's shadow fleet, again vessels used to carry oil.

The EU said it is considering sanctions against the shadow fleet.

Reaction: Estonia, Finland and Baltic states

President Alar Karis said: "Repeated damage to Baltic Sea infrastructure signals a systemic threat, not mere accidents. Estonia will take action to counter this threat, together with #Finland and other NATO allies."

Finnish Prime Minister Petteri Orpo said it is too early to conclude that Moscow is behind the latest undersea cable disruptions in the Baltic Sea. However, Finland "will respond decisively" to any suspected interference with its undersea infrastructure.

Prime Minister Kristen Michal (Reform) thanked Orpo for "excellent cooperation" and said he was "glad" the suspected ship had been detained. "We need to step up our bilateral, NB8, EU and NATO cooperation to keep our critical cables secure," he wrote on social media.

Minister of Foreign Affairs Margus Tsahkna said damage has become so frequent it is "difficult to believe this is accidental or merely poor seamanship."

"We must understand that damage to submarine infrastructure has become more systematic and thus must be regarded as attacks against our vital structures," he said in a statement, adding the shadow fleet is a "security threat."

Chairman of the Riigikogu's Foreign Affairs Committee Marko Mihkekson (Reform) said if the damage is caused by a vessel then NATO members should be consulted. "Closing the Baltic Sea to vessels flying certain flags should not be ruled out," he said.

MEP Urmas Paet (Reform) said the EU and NATO need to take "real steps" to protect infrastructure. "The phase of passive protocolization is over," he wrote.

Estonia's closest neighbors also stressed the frequency of undersea cable breakages.

President of Latvia Edgars Rinkevics said the damage is "most probably" not a coincidence "to put it nicely."

Lithuanian Minister of Foreign Affairs Kestutis Budrys said: "The growing number of undersea incidents in the Baltic Sea, affecting critical infrastructure, should serve as a stark & urgent warning to both NATO & EU."

He said it's "imperative" that critical infrastructure needs to be better protected.

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