The Balticconnector gas pipeline was shut early on Sunday on concerns that gas was leaking from a hole in the 77-km (48-mile) pipeline.
Finnish operator Gasgrid said it could take months or more to repair.
"It is likely that damage to both the gas pipeline and the communication cable is the result of outside activity.
The damage to the gas pipeline was believed to have taken place in Finnish waters, while the telecoms cable breach was in Estonian waters, Finnish authorities said.
Prices were already up on Tuesday due to fears over tensions in the Middle East but expectations that outside activity caused the pipeline damage pushed prices in the nervous market higher.
Persons:
Jens Stoltenberg, Gasgrid, Sauli Niinisto, Petteri Orpo, Orpo, Elisa, Timo Kilpelainen, Terje Solsvik, Anne Kauranen, Anna Ringstrom, Andrius, Marta Frackowiak, Louise Rasmussen, Susanna Twidale, Julia Payne, Bart Meijer, Gwladys Fouche, Susan Fenton, Jonathan Oatis
Organizations:
Finnish Border Guard, Companies Gas, PM, NATO, Reuters, Finnish, Amber Grid, Thomson
Locations:
of Finland, Estonian, Finland, Estonia, HELSINKI, Baltic, Finnish, Inkoo, Paldiski, St Petersburg, NORD, Russia, Germany, Latvia, Lithuania, Lithuanian, Ukraine, United States, Latvian, Hamina, Oslo, Helsinki, Stockholm, Andrius Sytas, Vilnius, Gdansk, Copenhagen, London, Brussels