Denmark believes "deliberate actions" caused big leaks in two natural gas pipelines running under the Baltic Sea from Russia to Germany, and seismologists said powerful explosions preceded the leaks.

European leaders and experts pointed to possible sabotage amid the energy standoff with Russia provoked by the war in Ukraine. Although filled with gas, neither pipeline is currently supplying it to Europe.

"It is the authorities' clear assessment that these are deliberate actions -- not accidents," Danish Prime Minister Mette Frederiksen said Tuesday.

But she added "there is no information indicating who could be behind it." Frederiksen rejected the suggestion that the incident was an attack on Denmark, saying the leaks occurred in international waters.

The incident overshadowed the inauguration of a long-awaited pipeline that will bring Norwegian gas to Poland to bolster the continent's energy independence from Moscow.

The first explosion was recorded early Monday southeast of the Danish island of Bornholm, said Bjorn Lund, director of the Swedish National Seismic Network. A second, stronger blast northeast of the island that night was equivalent to a magnitude-2.3 earthquake. Seismic stations in Denmark, Norway and Finland also registered the explosions.

"There's no doubt, this is not an earthquake," Lund said.

On Wednesday, Danish defense minister Morten Bødskov will travel to Brussels to discuss the leaks with NATO chief Jens Stoltenberg.

Denmark's Foreign Minister Jeppe Kofod said Sweden, Germany and Poland have been kept informed, and "we will inform and reach out to Russia in this case."

He said Denmark's foreign intelligence service didn't see any increased military threat against Denmark after the three leaks on the Nord Stream 1 and 2 pipelines.

They created a foamy white area on the water's surface, images released by Denmark's military show. Danish Energy Minister Dan Jørgensen said that "we cannot say how long the leak will go" on for as the gas has not been turned off. There was no indication when the gas would be turned off.

The German operator of the pipelines, Nord Stream AG, said it's preparing a survey to assess the damage.

"Currently, it is not possible to estimate a timeframe for restoring the gas transport infrastructure," a company statement said. "The causes of the incident will be clarified as a result of the investigation."

In Sweden, acting Prime Minister Magdalena Andersson said "it is probably a case of sabotage," but not an attack on Sweden.

Andersson added that neighboring oil-rich Norway "has informed us about increased drone activity in the North Sea and the measures they have taken in connection with it."

Foreign Minister Ann Linde said that Sweden "(is) not ruling out any scenarios and we will not speculate about motive or actor."

The escaped natural gas is made up almost entirely of methane - the second biggest contributor to climate change after carbon dioxide. David Hastings, a retired chemical oceanographer in Gainesville, Florida, said much of the gas would rise through the sea and enter the atmosphere. "There is no question that the largest environmental impact of this is to the climate, because methane is a really potent greenhouse gas," he said.

According to United Nations data, methane is 82.5 times worse for the climate than carbon dioxide over a 20-year period, because it so effectively absorbs the heat of the sun.

Polish Prime Minister Mateusz Morawiecki called the events "an act of sabotage." During a ceremony in northwestern Poland, Morawiecki, Denmark's Frederiksen and Polish President Andrzej Duda symbolically opened the valve of a yellow pipe belonging to the Baltic Pipe, a new system sending Norwegian gas across Denmark to Poland.

"The era of Russian domination in the gas sphere is coming to an end," Morawiecki declared. "An era that was marked by blackmail, threats and extortion."

No official presented evidence of what caused the leaks, but with distrust of Russia running high, some feared Moscow sabotaged its own infrastructure out of spite or to warn that pipelines are vulnerable to attack. The leaks raised the stakes on whether energy infrastructure was being targeted and led to a small bump in natural gas prices.

"We can clearly see that this is an act of sabotage, an act that probably means a next step of escalation in the situation that we are dealing with in Ukraine," Morawiecki said.

Secretary of State Antony J. Blinken spoke with Danish Foreign Minister Jeppe Kofod about the apparent sabotage, according to State Department spokesperson Ned Price, who reiterated the U.S. was committed to promoting European energy security.

Anders Puck Nielsen, a researcher with the Center for Maritime Operations at the Royal Danish Defence College, said the timing of the leaks was "conspicuous" given the ceremony for the Baltic Pipe. He said perhaps someone sought "to send a signal that something could happen to the Norwegian gas."

The extent of the damage means the Nord Stream pipelines are unlikely to be able to carry any gas to Europe this winter even if there was political will to bring them online, analysts at the Eurasia Group said. Russia has halted flows on the 1,224-kilometer (760-mile) Nord Stream 1 pipeline during the war, while Germany prevented them from ever starting in the parallel Nord Stream 2.

"Depending on the scale of the damage, the leaks could even mean a permanent closure of both lines," analysts Henning Gloystein and Jason Bush wrote.

Puck Nielsen said of possible sabotage that "technically speaking, this is not difficult. It just requires a boat. It requires some divers that know how to handle explosive devices."

"But I think if we look at who would actually benefit from disturbances, more chaos on the gas market in Europe, I think there's basically only one actor right now that actually benefits from more uncertainty, and that is Russia," he said.

Asked if the leaks may have been caused by sabotage, Kremlin spokesman Dmitry Peskov said "no version could be excluded."

"This is an unprecedented situation that requires an urgent investigation. We are extremely worried by this news," he said in a conference call with reporters.

Danish and Swedish maritime authorities issued navigation warnings, and established a prohibited area for vessels. Ships may lose buoyancy, and there may also be a risk of ignition above the water and in the air.

The Nord Stream pipelines have been at the center of an energy clash between Europe and Russia since the invasion of Ukraine in late February. Plunging Russian gas supplies have caused prices to soar, pressuring governments to help ease the pain of sky-high energy bills for households and businesses as winter nears. The crisis also has raised fears of rationing and recession.

The Baltic Pipe is a prominent element in the European Union's search for energy security and is to start bringing Norwegian gas through Denmark and along the Baltic Sea to Poland on Oct. 1.

Simone Tagliapietra, an energy expert with the Bruegel think tank in Brussels, speculated that the leaks could have been caused by Russian sabotage or anti-Russian sabotage.

One possibility is Russia signaling it "is breaking forever with Western Europe and Germany" as Poland inaugurates its pipeline with Norway, he said.

"In any case, this is a stark reminder of the exposure to risk of Europe's gas infrastructure," Tagliapietra said.

From The Associated Press