Two explosions followed by three unexplained leaks took place at two key pipelines carrying natural gas from Russia to Europe this week, prompting claims of sabotage and concerns over energy safety on the continent.

The Nord Stream 1 and 2 leaks raise questions over their beneficiaries as winter looms and Europe continues to grapple with an energy crisis triggered by Russia’s invasion of Ukraine.

What happened?

Scandinavian seismologists recorded explosions in the Baltic Sea near the Danish island of Bornholm at 1:03 a.m. and 6:03 p.m. GMT Monday.

Around that time, Nord Stream’s operator reported a pressure drop on both strings of the pipeline, neither of which were operational. 

Russian state-owned energy giant Gazprom halted exports via Nord Stream 1 as of Aug. 31. Germany scrapped the Nord Stream 2 project, which in the days before Russia invaded Ukraine in February.

Denmark’s military published footage of the leak sending gas bubbling to the surface of international waters in the Swedish and Danish economic zones.

The following day Tuesday, officials attended the opening ceremony for Baltic Pipe, a new pipeline carrying Norwegian gas to Poland via Denmark, seen as part of the European Union’s efforts to reduce its dependence on Russian energy.

What do Russia and Ukraine say?

The Kremlin said Tuesday it was “extremely concerned” about the “unprecedented situation” and said no theory of what caused the leaks, including sabotage, could be ruled out before an investigation established their cause.

Russian state media suggested Ukraine and the United States may have been behind the explosions, citing as evidence a tweet by Poland’s former foreign minister saying “thanks USA” alongside an image of the leaking gas.

Russian Foreign Ministry spokeswoman Maria Zakharova appeared to lean into the theory, asking European leaders for clarification of the tweet. The Kremlin said Wednesday it also noted Polish officials’ “euphoria” over the leaks and “huge profits” from U.S. gas supplies to Europe.

The United States said it was looking at reports of an attack or sabotage, vowing support for Europe’s energy security.

European leaders were nearly unanimous in the conclusion that the explosions are an act of sabotage, though they were reluctant to point fingers.

Ukrainian leaders blamed Russia, saying the explosions were “nothing more than a terrorist attack planned by Russia and an act of aggression towards the EU.”

The CIA had warned Germany over the summer of possible acts of sabotage on the Nord Stream pipeline, Germany’s Spiegel magazine reported.

The Kremlin said Wednesday that Moscow would welcome a joint investigation with the EU if approached, calling it “stupid and absurd” to suspect that Russia was behind the leaks.

The Foreign Ministry in Moscow said U.S. President Joe Biden is “obliged” to answer if Washington is behind the reported gas leaks.

“On Feb. 7, 2022, Joe Biden said that Nord Stream would be finished if Russia invaded Ukraine… Biden is obliged to answer the question of whether the U.S. carried out its threat,” Foreign Ministry spokeswoman Maria Zakharova said on social media.

Later Wednesday, Zakharova said Russia will ask for the United Nations Security Council to convene over the leaks.

Why is Nord Stream important?

The Nord Stream 1 and 2 pipelines have been a major source of geopolitical tensions in recent months as Russia has gradually slashed gas supplies to Europe in suspected retaliation against Western sanctions over Moscow’s invasion of Ukraine.

President Vladimir Putin has called for Europe to lift sanctions on Nord Stream 2 to allow gas to flow to the continent.

Nord Stream 1 had accounted for 40% of the European Union’s gas supplies via Germany, keeping energy costs low in the EU’s largest economy.

With a capacity of carrying 170 million cubic meters of gas per day, Russia had cut flows to 20% before halting the pipeline’s operations altogether.

Nord Stream 2 was due to double export capacities to 110 billion cubic meters, but the project never received authorization due to Russia’s recognition of Ukraine’s breakaway regions as independent states ahead of Moscow’s full-scale invasion.

Denmark’s defense minister said Wednesday it could take up to two weeks to inspect the Nord Stream leaks due to pressure inside the pipes. Russian analysts, citing past cases, expect repairs to take several years.

German officials fear that both Nord Stream pipelines could be permanently unusable, the Tagesspiegel newspaper reported. The ability to save the pipelines will depend on the amount of salt water that has entered the tubes and corroded their insides, the newspaper said.

AFP contributed reporting.