Finnish Border Guard's ship Turva and oil tanker Eagle S sail on the sea outside the Porkkalanniemi, Finland on December 26, 2024. (RAJAVARTIOSTO-Finnish Border Guard/LEHTIKUVA/HANDOUT via REUTERS/File Photo)

Finland on Thursday seized a ship on suspicion of causing an outage of the Estlink 2 undersea power cable linking it with Estonia, and of disrupting fibre optic lines. On Friday it said it had asked the transatlantic military alliance for support.

"We have agreed with Estonia, and we have also communicated to NATO Secretary General Mark Rutte, that our wish is to have a stronger NATO presence," Finnish President Alexander Stubb told a news conference.

Rutte posted on the social media platform X that "NATO will enhance its military presence in the Baltic Sea", without elaborating. 

Sweden's coastguard said it had increased surveillance of ship traffic, deploying aircraft and vessels and coordinating with other nations.

"If there is a threat to the critical undersea infrastructure in our region, there will also be a response," Foreign Minister Margus Tsahkna said on X.