The explosions that damaged the Nord Stream 1 and 2 gas pipelines, causing leaks into the Baltic Sea, appear to be the "result of a deliberate act," the European Union said Wednesday.

European Commission President Ursula von der Leyen said investigations are underway into what she called "sabotage action," vowing that deliberate disruption of European energy infrastructure would "lead to the strongest possible response."

Several European leaders said the explosions that caused leaks in the undersea natural gas pipelines appeared to be sabotage, as the E.U. put out a statement vowing to respond. "These incidents are not a coincidence and affect us all," the bloc said. Five European officials with direct knowledge of security discussions said it is widely assumed that Russia was behind the incident.

The Kremlin has denied responsibility for the explosions, stating that it was not in Russia's economic interest to damage the pipelines. Spokesman Dmitry Peskov said it was "absurd" to blame Moscow, adding "this is a big problem for us." He accused the United States of making "super profits" from European energy disruption. Speaking under the condition of anonymity to discuss the sensitive matter, a U.S. official said the United States had nothing to do with the attack on the Nord Stream pipeline, calling the idea "preposterous."

Norway said it would increase security around its oil and gas infrastructure, while Swedish, Danish and German authorities have all opened investigations into the blasts. NATO Secretary General Jens Stoltenberg said he met Wednesday with Denmark's defense minister to discuss the "sabotage" and emphasized that "protection of critical infrastructure" in NATO countries remains paramount. Russia said it would consider participating in a joint investigation with European officials into the incidents but complained that it has not been approached.

The damage did not have an immediate impact on Europe's energy supplies. Russia cut off flows earlier this month, and European countries had scrambled to build up stockpiles and secure alternative energy sources before that.

But the episode is likely to mark a final end to the Nord Stream pipeline projects, a more-than-two-decade effort that deepened Europe's dependence on Russian natural gas — and that many officials now say was a grave strategic mistake.

The pair of explosions Monday produced leaks in all three of the underwater Nord Stream pipelines that connect Russia and Germany, causing massive plumes of gas bubbles to break the surface of the Baltic Sea.

"These are deliberate actions, not an accident," Danish Prime Minister Mette Frederiksen told reporters Tuesday. "The situation is as serious as it gets."

Frederiksen said the explosions, just off the coast of the Danish island of Bornholm, were not "an attack on Denmark," since they took place in international waters. But Danish military leaders on Tuesday dispatched the Absalon, one of their top-of-the-line frigates, along with other patrol ships, to guard the island. Danish Foreign Minister Jeppe Kofod was calling other NATO counterparts to discuss the situation, according to a senior European diplomat who was familiar with the conversations and who, like others, spoke on the condition of anonymity to talk frankly about internal security.

"We do not know the details of what happened yet, but we can clearly see that it is an act of sabotage," Polish Prime Minister Mateusz Morawiecki told reporters Tuesday.

The act "probably marks the next stage in the escalation of this situation in Ukraine," Morawiecki said. He was speaking at a ceremony to open the new Baltic Pipe undersea pipeline that gives Poland and its neighbors access to Norwegian natural gas. The project was intended to reduce dependence on the gas that once flowed from Russia.

Five European officials with direct knowledge of security discussions said there was a widespread assumption that Russia was behind the incident. Only Russia had the motivation, the submersible equipment and the capability, several of them said, though they cautioned that they did not yet have direct evidence of Russia's involvement.

"No one on the European side of the ocean is thinking this is anything other than Russian sabotage," said a senior European environmental official, speaking on the condition of anonymity to discuss internal thinking about the leak.

One official said it might have been a message to NATO: "We are close." Another said that it could be a threat to other, non-Russian energy infrastructure, since so many pipelines crisscross the Baltic Sea, including the one inaugurated Tuesday. A third noted that crucial internet data cables lie along the bottom of the sea, and there have been long-standing concerns that Russia has a submersible program that could cut them, causing communications chaos around the world.

Although gas was not being sent to Europe through the pipelines, there appeared to be a significant amount that remained in the pipes, raising concerns about possible environmental harm from methane — the main component of natural gas and a major contributor to climate change when it manages to reach the atmosphere.

Danish Climate Minister Dan Jorgensen told reporters that it might take at least a week to halt the flow of gas to the surface of the Baltic Sea.

Two of the damaged pipes are part of Nord Stream 1, which was previously a major transmission line of Russian natural gas to Germany, Poland and other European nations. Russia decreased and then stopped the flows through Nord Stream 1 earlier this year. The Kremlin blamed technical problems. European leaders, including European Commission President Ursula von der Leyen, accused the Kremlin of using fossil fuels to "blackmail" countries supporting Ukraine.

The third leak is part of the newer Nord Stream 2, a project that Germany froze as Russia launched its invasion.

The Swedish National Seismic Network (SNSN) registered two distinct blasts in the vicinity of Bornholm on Monday. Automatic monitoring picked up the first blast, which registered the equivalent of an earthquake magnitude of 1.8, at 2:03 a.m. A second, larger blast, registering an equivalent earthquake magnitude of 2.3, came at 7:04 p.m.

"The location of the second blast is five or six kilometers away from where the Swedish Maritime Administration puts the gas leak," said Bjorn Lund, director of the Swedish seismic network. He noted that the complexity of the geographic area means there is some deviation in any estimated distance.

SNSN often registers blasts in the area when the Swedish navy conducts explosive exercises, Lund said, and consequently has a lot of data on the surrounding area.

"That [comparative data] make us even more sure that these are blasts and not earthquakes or landslides or something more natural," he said. "What we see now is very similar to what we recorded for these navy blasts."

The German Research Center for Geosciences confirmed similar findings to The Washington Post, saying it was certain that the seismic disturbances were not caused by a naturally occurring earthquake.

Imagery provided to The Post by Planet Labs, an Earth imaging company, showed methane bubbles appearing on the surface as early as 9 a.m. Monday, following the first recorded blast.

A spokesman for the European Commission said that although gas supplies were not at risk, officials were concerned about potential environmental damage.

"This hasn't affected the security of supply as yet," spokesman Tim McPhie said. "Deliveries have been zero on Nord Stream 1 anyway, and Nord Stream 2 is not yet authorized to operate. We are also analyzing the potential impact of these leaks of methane, which is a gas which of course has considerable effects on climate change, and we are in touch with the member states about the potential impact on maritime navigation."

The potential environmental impact was hard to assess, experts said, because the amount of methane actually released into the atmosphere depends on a wide range of variables. Methane is more than 80 times more potent than carbon dioxide for the first 20 years after it is released into the atmosphere. But water is able to absorb at least part of the gas when it is released underwater.

"We don't know the volume of methane coming out, we don't know how long it's going to continue, we don't know the size of the bubbles that are being formed as it comes out," all of which is key to understanding how much methane might be released, said Carolyn Ruppel, chief scientist for the U.S. Geological Survey's Gas Hydrates Project.

Scientists said that the relatively shallow depth of the pipeline — roughly 75 yards below the water's surface — was concerning.

"In a shallow situation like this, it is much more likely that substantial amounts of the methane can reach the atmosphere," Ruppel said.

The Washington Post's Meg Kelly and Michael Birnbaum in Washington, Mary Ilyushina from Riga, Latvia, Kate Brady in Berlin, Beatriz Rios in Brussels, John Hudson in Washington, and Kareem Fahim and Zeynep Karatas contributed to this report.