The Swedish navy encounters Russian submarines in the Baltic Sea on an “almost weekly” basis, its chief of operations has said, and is preparing for a further increase in the event of ceasefire or armistice in the Ukraine war.

Capt Marko Petkovic said Moscow was “continuously reinforcing” its presence in the region, and sightings of its vessels were a regular part of life for the Swedish navy. Its “very common”, he said, adding that the number of sightings had increased in recent years.

Sweden recently hosted a major Nato anti-submarine warfare exercise, Playbook Merlin 25, featuring nine countries, including Sweden, Germany, France and the US, in which hundreds of personnel practised their submarine-hunting skills in the unique conditions of the Baltic to prepare for possible underwater attack.