The US said it was ready to help European allies on energy security after leaks were detected on the Nord Stream pipelines.
The US Secretary of State Antony Blinken said the he was looking at reports that the leaks were the result of an attack or some kind of sabotage.
"If it is confirmed, that's clearly in no one's interest.
"My understanding is the leaks will not have a significant impact on Europe's energy resilience," he said.
But he added: "What's critical is that we are working day-in day-out, both on a short term basis and a long term basis, to address energy security for Europe and, for that matter, around the world."
He pointed to US efforts to step up shipments of liquified natural gas since Moscow's invasion of Ukraine as US allies, notably Germany, tried to reduce their reliance on Russian energy.
Ukraine accused Russia of causing the leaks on the Nord Stream 1 and Nord Stream 2 pipelines, saying the alleged actions amount to "nothing more than a terrorist attack."
Earlier, European Commission President Ursula von der Leyen said that the leaks on the Nord Stream gas pipelines in the Baltic Sea were an "act of sabotage".
"Any deliberate disruption of active European energy infrastructure is unacceptable and will lead to the strongest possible response," she said, adding it was "paramount to now investigate the incidents, get full clarity on events & why."
Her comments come as Europe is investigating what Germany and Denmark said were attacks that had caused major leaks into the Baltic Sea from two Russian pipelines at the centre of an energy standoff.
But it remained far from clear who might be behind the leaks, if proven, on the Nord Stream pipelines that Russia and European partners spent billions of Euro building.
German Economy Minister Robert Habeck told business leaders that the leaks were due to targeted attacks on the infrastructure and Berlin now knew for sure "that they were not caused by natural occurrences or events or material fatigue".
Poland's Prime Minister blamed sabotage, without citing evidence, Denmark's Prime Minister said the leaks were clearly caused by deliberate actions and Swedish police said they had begun an investigation into potential "gross sabotage".
"It is now the clear assessment by authorities that these are deliberate actions. It was not an accident," Mette Frederiksen said at a press briefing in Copenhagen.
The Danish government expects the leaks at the pipelines, which are not operational but full of gas, will last "at least a week" - until the methane escaping from the underwater pipes runs out, the Danish energy and climate minister said at a press conference.
Russia, which slashed gas deliveries to Europe after the West imposed sanctions over Moscow's invasion of Ukraine, also said sabotage was a possibility and that the leaks undermined the continent's energy security.
A senior Ukrainian official called the incident a Russian attack to destabilise Europe, without giving proof.
"We see clearly that it's an act of sabotage, related to the next step of escalation of the situation in Ukraine," Polish Prime Minister Mateusz Morawiecki said at the opening of a new pipeline between Norway and Poland.
Seismologists in Denmark and Sweden said they had registered two powerful blasts in the vicinity of the leaks.
"The signals do not resemble signals from earthquakes. They do resemble the signals typically recorded from blasts," the Geological Survey of Denmark and Greenland (GEUS) said.
Danish authorities assess that the damage was caused by blasts, Energy Minister Dan Jorgensen said at a press briefing.
He added that the size of the holes in the pipelines indicate that the leaks could not have been caused by an accident such as getting hit by an anchor.
Seismologists at Sweden's Uppsala University, which cooperates with GEUS, said the second, bigger explosion "corresponded to more than 100kg of dynamite", adding blasts were in the water not under the seabed.
The Nord Stream pipelines have been flashpoints in an escalating energy war between capitals in Europe and Moscow that has damaged major Western economies, sent gas prices soaring and sparked a hunt for alternative supplies.
"Germany is a country that knows how to defend itself. And Europe is a continent that can protect its energy infrastructure," Germany's Mr Habeck said, adding that the energy supply of Europe's largest economy was not affected.
Denmark's armed forces released video showing bubbles rushing to the surface of the Baltic Sea above the pipelines, and said the largest gas leak had caused surface disturbance of well over 1 kilometre in diameter.
US National Security Advisor Jake Sullivan tweeted to say he had spoken to his "counterpart Jean-Charles Ellermann-Kingombe of Denmark about the apparent sabotage of Nord Stream pipelines."
"The U.S. is supporting efforts to investigate and we will continue our work to safeguard Europe's energy security," he added.
'RISK OF EXPLOSIONS'
The leaks were very large and it could take perhaps a week for gas to stop draining out of the Nord Stream 2 pipeline, the head of Denmark's Energy Agency Kristoffer Bottzauw said.
Ships could lose buoyancy if they entered the area.
"The sea surface is full of methane, which means there is an increased risk of explosions in the area," Mr Bottzauw said.
The Swedish Maritime Administration (SMA) said two leaks on Nord Stream 1, one in the Swedish economic zone and another in the Danish zone, were northeast of Denmark's Bornholm.
"We are keeping extra watch to make sure no ship comes too close to the site," an SMA spokesperson said.
Danish Prime Minister Mette Frederiksen said sabotage could not be ruled out. "We are talking about three leaks with some distance between them, and that's why it is hard to imagine that it is a coincidence," she said.
Kremlin spokesperson Dmitry Peskov called it "very concerning news. Indeed, we are talking about some damage of an unclear nature to the pipeline in Denmark's economic zone." He said it affected the continent's energy security.
Neither pipeline was pumping gas to Europe at the time the leaks were found, but the incidents will scupper any remaining expectations that Europe could receive fuel via Nord Stream 1 before winter.
Operator Nord Stream said the damage was "unprecedented".
Gazprom, the Kremlin-controlled company with a monopoly on Russian gas exports by pipeline, declined comment.
"There are some indications that it is deliberate damage, "said a European security source, adding it was still too early to draw conclusions. "You have to ask: Who would profit?"
Norway, meanwhile, said it will strengthen security at its oil and gas installations in the wake of leaks and reports of drone activities in the North Sea, its Energy Minister Terje Aasland said in a statement.
Authorities in Denmark asked that the level of preparedness in its power and gas sector be raised, a step that would require heightened safety for power installations and facilities.
CUTTING SUPPLIES
Russia reduced gas supplies to Europe via Nord Stream 1 before suspending flows altogether in August, blaming Western sanctions for causing technical difficulties. European politicians say that was a pretext to stop supplying gas.
The new Nord Stream 2 pipeline had yet to enter commercial operations. The plan to use it to supply gas was scrapped by Germany days before Russia sent troops into Ukraine, in what Moscow calls a "special military operation", in February.
"The multiple undersea leaks mean neither pipeline will likely deliver any gas to the EU over the coming winter, irrespective of political developments in the Ukraine war," Eurasia Group wrote in a note.
European gas prices rose on the news, with the benchmark October Dutch price climbing almost 10% on Tuesday. Prices are still below this year's peaks but remain more than200% higher than in early September 2021.
