Russian spy vessels are mapping offshore critical infrastructure in the Nordics including wind farms, gas pipelines, power and internet cables, the public Danish Broadcasting Corporation (DR) reported.

A large number of military and civilian ships sailing in waters around Denmark, Norway, Finland and Sweden are trying to discover how infrastructure is connected, the broadcaster in collaboration with Norwegian, Swedish and Finnish television stations claimed in a documentary series dubbed ‘The Shadow War’.

Russia’s aim is to plan sabotage against the Nordic countries, including by being able to cut power and data cables across the Atlantic and to the rest of Europe, sources are said to have told the TV stations.

“In the event of a conflict with the West, they are ready and know where to intervene if they want to paralyse Danish society,” counterintelligence chief Anders Henriksen from the Danish Police Intelligence Service (PET) is quoted as saying on DR.

Russian so-called ‘ghost ships’ are sailing in Nordic waters with their AIS transmitters turned off in order not to share their locations, the TV stations claim, pointing to the Russian vessel Admiral Vladimirsky sailing through waters in Denmark's exclusive economic zone in the Kattegat that connects the North and Baltic Seas.

While the vessel’s AIS transmitter was turned off, the Admiral Vladimirsky continuously sent radio messages to a naval base in Russia containing its positions, DR said, which sailed out to the ship with a journalist and photographer near Sjaellands Odde and Grenaa in Danish waters.

Their rubber boat was met with a uniformed and masked man wearing a bulletproof vest armed with a Russian military rifle, the broadcaster said, also showing video footage of that on its website.

The TV stations added that the vessel has sailed around the Baltic Sea, Great Belt, Kattegat and North Sea for a month.

The Admiral Vladimirsky may also have been the vessel that was seen observing offshore wind farms in Belgian and Dutch waters earlier. It is one of some 50 Russian vessels that have sailed in suspicious manner over the past ten years, the broadcasters said.

The head of the Dutch military intelligence, general Jan Swillens, in February went on the record saying the Russians were engaged in “activities that indicate espionage as well as preparing operations for disturbance and sabotage.”

"Russia is mapping how our wind parks in the North Sea function. They are very interested in how they could sabotage the energy infrastructure."

Asked by DR about the recent suspicious activities by Russian ships, the country’s ambassador to Norway claimed the work of research vessels is in demand and being carried out in full compliance with international law.

But CR points to a ‘central source in a Western intelligence service’ claiming that those ships are preparing sabotage “as part of the preparation for a major war with NATO”.