The navies of Britain, Finland and Estonia were practising subsea infrastructure protection in the Baltic Sea region on Monday together with the Finnish Border Guard, Finland's Defence Forces said in a statement.
In early October a gas pipeline linking Estonia and Finland was damaged along with three telecommunications cables in the area, which is known for its dense seabed infrastructure.
Finland and Estonia suspect the gas pipeline and cable incidents are linked, and believe a Hong Kong-flagged container carrier caused the damage by dragging its anchor along the seabed. China has said it is willing to provide necessary information in accordance with international law.
The aim of the joint exercise, which continues on Tuesday, is to develop capabilities for the surveillance and protection of undersea infrastructure and to repel subsea military threats, Finland said.
"After the Balticconnector incident, many countries of the Baltic Sea region have increased their cooperation and their own national maritime surveillance operations," Commodore Janne Huusko of the Finnish Defence Command said.
All three participants are members of the NATO military alliance but the exercise is taking place under their Joint Expeditionary Force (JEF) defence cooperation, which encompasses the Nordic and Baltic states, the Netherlands and Britain.
Britain said on Thursday it would send seven Royal Navy ships and a maritime patrol aircraft to take part in JEF patrols in the region in December.
In October, Britain had said it planned to step up its military presence in Northern Europe, including deploying 20,000 troops to the region next year, to help protect critical infrastructure at a time of growing concern over Russian sabotage.
The Baltic Sea was also the scene last year of the destruction of the Nord Stream gas pipelines from Russia to Germany, which investigators say were deliberately blown up, although they have not yet named a suspect.
(Reuters - Reporting by Anne Kauranen; Editing by Kirsten Donovan)