A Norwegian-owned and Russian-crewed ship that authorities initially suspected may have been involved in damage to an underwater fiber optic cable connecting Latvia and the Swedish island of Gotland has been released.

Nato countries have stepped up patrols to protect critical underwater infrastructure in the Baltic Sea, which is bordered by eight countries, and other waters. A Royal Navy submarine was ordered to surface last November close to a suspected Russian spy ship which was loitering over undersea infrastructure in UK waters.