Suspicious leaks in two Russian gas pipelines in the Baltic Sea are probably the result of sabotage, officials in Denmark, Germany and Poland have warned, heightening concerns over the vulnerability of Europe’s energy infrastructure.

Denmark’s prime minister Mette Frederiksen said sabotage could not be ruled out as the cause of leaks in the Nord Stream 1 and 2 pipelines, which have been at the centre of the energy conflict between Russia and Europe.

“It is too early to conclude yet, but it is an extraordinary situation,” she said. “There are three leaks and therefore it is difficult to imagine that it could be accidental.”

She later said there was no increased military threat to her country. “These are deliberate actions, not an accident,” she added.

German officials expressed concern that the sudden loss of pressure in both pipelines could be the result of a “targeted attack”. They added that Russia’s involvement could “not be excluded”, but said Germany was not involved in the investigation being run by Denmark and Sweden.

US national security adviser Jake Sullivan and secretary of state Antony Blinken spoke with their Danish counterparts on Tuesday about the suspicious leaks of the pipelines, which Sullivan described as “apparent sabotage”.

“The US is supporting efforts to investigate and we will continue our work to safeguard Europe’s energy security,” Sullivan later wrote on Twitter.

Ned Price, US state department spokesperson, also described the attacks as “apparent sabotage” in a statement late on Tuesday.

Price said Blinken spoke with Denmark’s foreign minister Jeppe Kofod, adding: “The United States remains united with our allies and partners in our commitment to promoting European energy security.”

The leaks come as Russian gas supplies to Europe have dwindled as part of President Vladimir Putin’s efforts to deter support for Ukraine. The leaks, which will not directly affect Russian gas flows because the pipelines were not operating, coincided with the inauguration of a pipeline that will deliver Norwegian gas through Denmark to Poland for the first time.

“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,” said Poland’s prime minister Mateusz Morawiecki, Reuters reported.

Mykhailo Podolyak, an adviser to Ukraine’s president Volodymyr Zelenskyy, wrote on Twitter: “‘Gas leak’ from NS-1 is nothing more than a terrorist attack planned by Russia and an act of aggression towards [the] EU. Russia wants to destabilise [the] economic situation in Europe . . . The best response and security investment — tanks for Ukraine. Especially German ones.”

Asked if sabotage was the cause of the leak, Kremlin spokesperson Dmitry Peskov told reporters that “no version can be excluded now”, Russian agency Interfax reported. “Obviously, the pipe has been damaged somehow. What the cause was — before the results of the investigation appear — no version can be excluded,” he added.

Sweden’s maritime administration on Tuesday reported two leaks in the Nord Stream 1 pipeline close to the Danish island of Bornholm in the Baltic Sea. That report came hours after Denmark’s energy agency said there was a separate leak, also close to Bornholm, in the Nord Stream 2 pipeline, which Germany effectively cancelled shortly before Russia’s full-scale invasion of Ukraine.

Nord Stream 2 had been filled with Russian gas at the end of last year in preparation for its planned start-up, while Nord Stream 1 was transporting gas to Germany as recently as the start of this month.

Danish authorities said the gas bubbles in the Baltic Sea measured about 1km in diameter. Sweden and Denmark warned ships to avoid the area.

Sweden’s National Seismology Centre said it had detected two powerful blasts the day before in the area of the gas leaks. “There is no doubt that these were explosions,” Björn Lund, a member of the seismic network, told Swedish state broadcaster SVT.

Terje Aasland, Norway’s oil and energy minister, said that as the leaks resembled sabotage, the country was paying close attention to security, on the day that it opened a gas pipeline to Poland.

Norway’s petroleum safety authority had warned on Monday that several oil and gas companies had recently complained of unidentified drones close to their offshore facilities. In June, a Russian warship twice violated Danish territorial waters near Bornholm.

Energy analysts said it was not clear who would stand to benefit from the leaks at a time when neither line was operational. But some suspected a connection to the new gas pipeline link. Frederiksen was in Poland on Tuesday for the opening ceremony.

“The leak on Nord Stream 2 is very close to the new Baltic pipe that will bring Norwegian gas to Poland for the first time . . . so there’s some heavy symbolism,” said Tom Marzec-Manser at energy consultancy ICIS. “For EU gas imports, it’s a new dawn for Norway and twilight for Russia.”

Ukraine has long opposed the Nord Stream pipelines, arguing that they were designed to weaken its position as one of the main conduits for Russian gas into Europe. Russian gas has continued to flow through Ukraine even after the invasion, but Moscow halted supplies through Nord Stream 1 last month, intensifying Europe’s energy crisis.

James Huckstepp at S&P Global Platts said the leaks increased uncertainty in the energy market. “The probability of Nord Stream 1 coming back before the end of the year has essentially dropped from 1 per cent to zero per cent,” he said. “But there remain concerns about the remaining gas flows through Ukraine and whether they could see reductions later this year.”

Henning Gloystein at Eurasia Group said the pipelines “are designed to avert accidental damage”. But he added: “Given both lines were still pressured and each has the capacity to pipe around 165mn cubic metres of methane-heavy gas a day, leaks of this size are a severe safety and environmental hazard.”

Nord Stream, the pipelines’ Swiss-based operator whose majority shareholder is Russian state-owned energy company Gazprom, said the incidents were “unprecedented”, but suggested most of the leaking methane would dissolve in the water.

Additional reporting by Felicia Schwartz in Washington