The Christmas Day cutting of four Internet cables and one power cable will cause NATO to boost its presence in the Baltic Sea.
Finland last week seized the Eagle S ship, carrying Russian oil, under suspicion of being behind the cuts.
“NATO will enhance its military presence in the Baltic Sea,” NATO secretary general Mark Rutte said.
Finland’s president, Alexander Stubb, added: “We have agreed with Estonia, and... our wish is to have a stronger NATO presence."
Three of the Internet cables that were cut, as well as the 658MW Estlink 2 cable, connected Finland and Estonia.
Estonia has launched a naval operation to protect the remaining 358MW Estlink 1 cable. "If there is a threat to the critical undersea infrastructure in our region, there will also be a response," the country's foreign minister Margus Tsahkna said.
Finnish forces have boarded the Eagle S, with investigations still ongoing. Lloyd's List reports that the tanker was carrying suspiciously hi-tech equipment, abnormal for a merchant ship, including “many laptops” that had keyboards for Turkish and Russian languages.
Investigators said that they found a seabed drag mark stretching almost 100km (about 60 miles) around the site of the cut electricity cable.
“Our current understanding is that the drag mark in question is that of the anchor of the Eagle S,” the police chief investigator, Sami Paila, told the Finnish national broadcaster Yle. “We have been able to clarify this matter through underwater research."
Estonia plans to decouple its power grid from the legacy Soviet network this spring and connect to the central European network instead.
The cable cut is expected to take months to fix and lead to higher electricity costs for Estonians.
This incident comes just a month after a ship was suspected of deliberately dragging an anchor 111 miles along the sea bed to sever two subsea cables in the Baltic Sea. That ship was also boarded, and investigations are ongoing.
Last month, a terrestrial Internet cable connecting Sweden and Finland was cut in two separate locations.