Gas is pouring into the Baltic Sea from three separate leaks on the Nord Stream 1 and 2 pipelines amid claims by seismologists in Sweden and Denmark of two sharp spikes in undersea activity, possibly indicating explosions, and speculation about sabotage. A seismograph on the Danish island of Bornholm, near where the leaks occurred, twice recorded spikes on Monday, the day on which the Nord Stream 1 and 2 gas pipelines underwent dramatic falls in pressure, the German geological research centre GFZ said. A Danish military flight over the leaks brought back striking images from the ruptures, including one showing an area of bubbling gas a kilometre wide on the sea’s surface. The seismograph recorded near-silence until just after midnight GMT (2am local time), when there was a spike representing a tremor in the earth followed by a continuous hissing wave form. The pattern was repeated at 5pm GMT. Amid the speculation over sabotage, suspicion immediately turned to potential culprits – with fingers pointed at Russia, whose pipelines were hit, suggesting a further weaponisation of energy supplies to Europe in the midst of the conflict in Ukraine. Not least it was seen as a possible message about the vulnerability of other marine gas infrastructure. “There are some indications that it is deliberate damage. You have to ask: Who would profit?” one European security source told Reuters. GFZ declined to be drawn on whether the tremors recorded could have been the result of an explosion but scientists at the research centre ruled out the possibility that the leaks could have been caused by earthquakes. “There was a spike and then regular noise,” a GFZ spokesperson, Josef Zens, said. “We cannot say if that could be gas streaming out.” A seismologist quoted by Swedish television suggested the activity may have been the result of explosions. Björn Lund, director of the Swedish National Seismic Network, SNSN, which measures Swedish earthquakes and explosions, told the SVT television channel that the event – one of which registered a magnitude of 2.3 – may have been caused by undersea detonations. “You can clearly see how the waves bounce from the bottom to the surface. There is no doubt that it was a blast. We even had a station in Gnosjö that picked this up,” said Lund, who also lectures in seismology at Uppsala University. Earlier, the Danish prime minister, Mette Frederiksen, said sabotage could not be excluded. Meanwhile the Kremlin spokesperson, Dmitry Peskov, called the news “very concerning” and said that “no option can be ruled out right now”, including sabotage. “This is a very concerning news,” he added, calling for a prompt investigation. “Indeed, we are talking about some damage of an unclear nature to the pipeline in Denmark’s economic zone.” The steel pipe itself has a wall of 4.1 cm (1.6 inches) and is coated with steel-reinforced concrete up to 11cm thick. Each section of the pipe weighs 11 tonnes, which goes to 24-25 tonnes after the concrete is applied. Among those pointing to the war in Ukraine was the Polish prime minister, Mateusz Morawiecki, who was speaking at the opening of a new gas pipeline between Norway and Poland. “Today we faced an act of sabotage. We don’t know all the details of what happened but we see clearly that it’s an act of sabotage, related to the next step of escalation of the situation in Ukraine,” Morawiecki said. Poland’s foreign minister was more forthright, suggesting that the damage could be an act of provocation on behalf of the Kremlin. “Sadly our eastern partner is constantly pursuing an aggressive political course,” the deputy foreign minister, Marcin Przydacz, said in Warsaw. “If it is capable of an aggressive military course in Ukraine, then it’s apparent that acts of provocations in western Europe also cannot be ruled out.” A senior Ukrainian official also called it a Russian attack to destabilise Europe, without giving proof. British sources said they believed it may not be possible to determine what occurred with certainty. One UK insider speculated that any explosions were unlikely to have been caused by a submarine or underwater vehicle, because their presence would have been detected in the relatively shallow Baltic waters. Sections of the pipelines are between 80 metres and 110 metres deep. An alternative scenario could be that mines were dropped from a disguised commercial vessel days or weeks ahead of the attack, then remotely detonated to cause the explosions. But the latter scenario was entirely hypothetical, they stressed. The day of drama began when the Danish energy agency said it had found the leaks on the Nord Stream 1 pipeline north-east of the island of Bornholm, and a third in the Nord Stream 2 pipeline in Swedish waters south-east of the island. “This is not a small crack. It’s a really big hole,” the energy agency said. Underlining the significance of the event, Javier Blas, an energy and commodities commentator for Bloomberg, described the undersea gas pipelines in the region as one of Europe’s most important strategic assets. “The subsea pipelines linking the North Sea gas fields, and then Norway with the rest of the continent and the UK are among the most strategic assets right now for Europe. High time for maximum protection. Cyber-attacks against energy assets are, too, a key risk for Europe,” Blas tweeted. A five-mile exclusion zone for shipping has been set up around Bornholm, and flights below 1,000 metres have been banned in the area. Methane, the primary component of natural gas, partially dissolves in water, is not toxic and creates no hazard when inhaled in limited quantities. “Breakage of gas pipelines is extremely rare”, Danish authorities said in a statement. “Therefore we see reason to raise the preparedness level as a result of the incidents we have seen over the past 24 hours.” Nord Stream AG, the pipeline operator, had on Monday morning reported an unexpected overnight drop of pressure from 105 to 7 bar in Nord Stream 2, which is filled with gas but was cancelled by Olaf Scholz, the German chancellor, shortly before Russia’s invasion of Ukraine. A further drop of pressure was reported on Monday afternoon in Nord Stream 1, which Russia shut down indefinitely at the start of September, initially saying it needed repairs. With three separate leaks almost simultaneously, with some distance between them, it was “difficult to imagine” it was a random accident, Frederiksen said at a short press conference during a visit to Poland, where she was participating in the opening of the Baltic Pipe gas pipeline. Anonymous sources in German government circles also said the simultaneity of the three leaks made an accident unlikely. “Our imagination cannot come up with a scenario which isn’t a deliberate attack,” a person involved in the investigation told the German daily Der Tagesspiegel. The news magazine Der Spiegel, quoting government sources, said officials were not ruling out sabotage, designed to cause further uncertainty on Europe’s energy markets. Since no gas has flowed through either of the pipelines since the start of the month, German authorities have been quick to reassure people that the leaks will not affect its plan to fill gas storage tanks in time for winter. Environmental NGOs said the leaks were likely to cause large-scale damage to the environment. “As soon as methane in gas form raises from the surface of the sea into the atmosphere, it will massively contribute to the greenhouse effect,” said Sascha Müller-Kraenner of the pressure group Environmental Action Germany.