Vladimir Putin could be planning to strike Europe's key infrastructure using deep-sea sabotage techniques after the Nord Stream pipeline was rocked by explosions, experts have warned.
Pipelines, rigs and undersea cables could be next on Russia's hit list as it tries cow Europe into ending support for Ukraine.
German interior minister Nancy Faeser said western European leaders needed to prepare for "previously unimaginable" threats while NATO draws up plans to "address the protection of critical infrastructure".
High up on Putin's target list could be two pipelines supplying Britain with vital oil from Norway.
Britain's largest oil and gas fields, which are fixed with dozens of rigs and pipelines and sit close to Norwegian waters and could also be targeted.
Putin's frogmen could also cut undersea cables carrying sensitive financial information and internet across the Atlantic, sparking an annihilating market crash, according to one US Navy sub warfare expert.
Meanwhile, Professor Damien Erns from the University of Liege in Belgium said Europe faced a "terrible recession" if any of its critical infrastructure were struck, adding protection systems are woefully unfit for purpose.
"Our infrastructure is not very well protected and it is extremely difficult to secure them over thousands of kilometres," he said.
"If gas supplies from Norway to Europe were cut off, we would see a terrible recession. We would not even be able to heat ourselves and produce electricity.
"The fears are very serious and well-founded. Europe has no more room for manoeuvre and we cannot exclude that things will deteriorate very significantly in the coming months."
Bryan Clark, a former US Navy strategic planner turned security expert, said efforts to survey the Batlic and North Sea could be eluded by Russia's state-of-the-art sabotage subs.
"It’s all part of the Russian style of political warfare," he said.
"It’s about sowing doubt, creating just enough fog of uncertainty."
It comes amid fears the Nord Stream gas line may have been damaged beyond repair could left crippled indefinitely after it was torn open by a series of explosions.
German officials reportedly believe the project - estimated to be worth around £35billion - may never be fully operational again.
It is feared the key gas network could have been sabotaged by Russia as tensions continue to rage with Europe over the war in Ukraine.
Twin 800-mile pipelines Nord Stream 1 and Nord Stream 2 can ferry 110billion cubic metres of gas annually from Russia into Western Europe.
Gas has not been flowing in recent weeks - and it is unclear at this stage how big an impact this will have on the European energy markets.
Prices had already spiked by up to 12 per cent following the apparent sabotage, deepening fears the continent is facing a cold and bleak winter.
German security services reportedly believe the damage has left the pipeline "forever unusable" - with three of four tubes so severely damaged they are now beyond repair, reports Tagesspiegel.
The paper reports the size of the holes in the pipes is sending large amounts of corrosive salt water flowing inside - further damaging them.
German government officials believe the complexity and scale of the attack could have only been carried out by a "state actor".
And the current theory is that Russia was behind it, even though "the motive is unclear".
European authorities are now desperately trying to piece together what exactly happened in the run up to the blasts just off the coast of Danish island Bornholm.
Nord Stream 2's single undamaged tube is now theoretically the only one which can now deliver gas - but the pipeline has not been operational for some time.
Massive leaks in the pipeline have left parts of the Baltic roiling with bubbles as residual gas leaks into the sea.
Two underwater explosions were detected on Monday alongside a mini earthquake.
Ukraine and Poland have pointed the finger at Moscow - while other European nations have stopped short of attributing blame.
Putin has been previously accused of weaponising the energy crisis in a bid to pile pressure on the West.
Russia has denied the allegations, calling them "predictable and stupid".
Professor Joan Cordiner, professor of process engineering at the University of Sheffield, said: "Pipes don't just leak catastrophically suddenly.
"Typically normal leaks due to corrosion start small and build up over time.
"Therefore such a sudden large leak can only have come from a sudden blow cutting the pipe."
Professor Michael Clarke, a security and defence analyst, told Sky News: "This is not some casual terrorist act, it has to be a government.
"The only government who could really gain from that, in a peculiar way, is Russia – none of the European governments would want to do it."
He added: "Privately, everyone is convinced this is a Kremlin-inspired piece of sabotage.
"This is a strategic own goal because although it increases the sense of isolation that there will be no Russian gas for Europe this winter, it actually destroys Russia's credibility completely with European customers for the next couple of generations."
Prof Clarke explained the Russians would want to "create insecurity" and warned there "may be more of this".
"It opens up a new front in the war. It means the Ukrainian war is now going to the Baltic," he warned.
If gas supplies from Norway to Europe were cut off, we would see a terrible recession. We would not even be able to heat ourselves and produce electricity
Professor Damien Erns
Europe is already braced for a bleak winter as gas becomes a key pawn in Putin's clash on the West.
Rolling blackouts, four day weeks, and normal people being unable to afford to heat their homes are just some of the consequences feared to sweep across the continent as temperatures plunge.
Gas prices were already high before the Ukraine war as demand soared after the lifting of Covid restrictions.
But prices skyrocketed after the invasion as Russia is one of the world's biggest producers.
Continental Europe is heavily reliant in Russian gas imports, leading to fears of winter blackouts, rationing and factory closures in Germany.
Only a tiny fraction of Britain's gas comes directly from Russia.
But the UK relies more on gas for generating electricity than European neighbours because it has less nuclear and renewable energy.
Britain also has little storage capacity, forcing energy firms to buy gas on the highly volatile short-term spot market.
Even the abundant North Sea gas is sold to the UK based on international market prices.
