Suspicious leaks in two gas pipelines running from Russia to Germany under the Baltic Sea caused a sudden drop in pressure on Monday, raising concerns about possible sabotage and prompting the authorities in Germany, Denmark and Sweden to investigate.
Sweden’s national seismic network said it detected two large undersea explosions on Monday near the locations of the leaks. Neither of the pipelines — Nord Stream 1 and 2 — had been active, but they were filled with gas when there was a sharp drop in pressure, first registered on Monday.
Footage released by the Danish Defense Command showed a swirling mass of methane bubbling up onto the surface of the Baltic Sea. Officials in Denmark raised its security alerts at electricity and gas facilities around the country.
Speculation immediately fell on Russia, which denied responsibility. The leaks underscored the vulnerability of Europe’s energy infrastructure, even as the continent tries to wean itself off supplies from the Russia as punishment for Moscow’s invasion of Ukraine.
Mateusz Morawiecki, Poland’s prime minister, blamed Russia for the leaks, saying they were an attempt to further destabilize Europe’s energy security. He spoke at the launch of a new undersea pipeline that connects Poland to Norway through Denmark.
“We do not know the details of what happened yet, but we can clearly see that it is an act of sabotage,” Mr. Morawiecki said. “An act that probably marks the next stage in the escalation of this situation in Ukraine.”
Denmark’s prime minister, Mette Frederiksen, said that sabotage could not be ruled out. “It is too early to conclude yet, but it is an extraordinary situation,” she said during a visit to Poland to inaugurate the pipeline from Norway.
“There is talk of three leaks, and therefore it is difficult to imagine that it could be accidental,” she said.
Mykhailo Podolyak, a senior adviser to President Volodymyr Zelensky of Ukraine, said on Twitter that the leaks were “a terrorist attack planned by Russia and an act of aggression towards E.U.”
The Kremlin’s spokesman, Dmitri S. Peskov, said of the leaks that “no possibility can be ruled out,” but the Russian state media sought to blame the United States and Ukraine. The state-run RIA Novosti news agency reported that Washington “is an active opponent of Russian gas supplies to Europe,” and said that Ukraine opposed Nord Stream 2 because it “was afraid of losing revenues from the transit of Russian gas.”
It was not immediately clear who would benefit from ruptures in the pipelines, which were not in operation. The leaks were found at different points on two branches of the Nord Stream 1 pipeline and one branch of Nord Stream 2, Danish and Swedish officials said. They warned ships to avoid the affected areas.
The pipelines have been a focal point of the broader confrontation between Russia and Europe. After the European Union imposed economic sanctions on Russia to penalize it for invading Ukraine in February, Russia began withholding the natural gas that for decades it had sent to Europe, threatening the continent’s energy supply as winter looms.
The governments in Denmark and Germany both said the leaks would not affect natural gas supplies in their countries. Gazprom had already halted nearly all deliveries of natural gas to Europe, through Nord Stream 1 as well as all but one of several overland pipelines, and European countries have turned to other suppliers, including Norway, to meet their energy needs.
But the incident made clear how vulnerable energy infrastructure could be. Norway’s Petroleum Safety Authority warned on Monday that unidentified drones had been sighted recently near its offshore oil and gas facilities, raising concerns of possible explosions, helicopter collisions or of “deliberate attacks.” It called for “increased vigilance by all operators and vessel owners,” citing the heightened security concerns following recent threats by Russia linked to its war in Ukraine.
Russia’s Gazprom halted deliveries through Nord Stream 1 indefinitely earlier this month, as part of a continuing dispute with Germany over gas deliveries. The pipeline is made up of about 100,000 concrete-coated steel pipes designed to withstand the change in pressure the gas undergoes on the 760-mile journey from Russia to Germany. They lie on the floor of the Baltic Sea.
Nord Stream 2 was never put into operation after Germany canceled its certification on the eve of Russia’s invasion of Ukraine.
Senators and members of Congress had lobbied for years to impose sanctions on Nord Stream 2. After Germany halted certification, President Biden imposed sanctions on the Russian-owned operator of the pipeline.
Monika Pronczuk, Oleg Matsnev and Torben Brooks contributed reporting.