The EU said on Wednesday that leaks from two undersea gas pipelines between Russia and Germany appear to be “a deliberate act” as fossil-fuel-rich Norway has tightened the security of its facilities.

The three outflows from the Nord Stream 1 and 2 pipelines have pushed up natural gas prices and exacerbated the energy crisis in Europe as winter approaches.

Methane gas from the leaks is bubbling to the surface of the Baltic Sea near Denmark and Sweden and is expected to continue for a week before the gas in the pipelines is exhausted.

Europa suspects the leaks are from sabotage.

They are “no coincidence,” EU foreign policy chief Josep Borrell said in a statement. “All available information indicates that these leaks are the result of a deliberate act.”

He warned: “Any intentional disruption of Europe’s energy infrastructure is absolutely unacceptable and will be met with a robust and unified response.”

Suspicion has centered on Russia, which cut off gas supplies to Europe in retaliation for tough Western sanctions over the war in Ukraine.

But the Kremlin hit back, saying it was “stupid and absurd” to blame Russia for causing the leaks.

EU leaders Ursula von der Leyen and Charles Michel have both blamed sabotage for the Nord Stream leaks.

Michel tweeted on Wednesday that they “appear to be an attempt to further destabilize the EU’s energy supply”.

He added: “Those responsible will be held fully accountable and asked to pay.”

The EU is currently considering further sanctions against Russia over annexation votes imposed on four regions in Ukraine occupied by its armed forces.

None of the Nord Stream pipelines are currently operational, but they were full of gas when they were hit by “massive releases of energy,” Swedish seismologists said.

One of the seismologists told AFP, “There isn’t much other than an explosion that could cause this.”

Danish Defense Minister Morten Bodskov told reporters in Brussels that “it could easily take a week or two for the area to settle down enough” for an inspection to verify the cause.

Two Danish military ships were sent to the area.

Non-EU member Norway, which has now overtaken Russia as Europe’s biggest gas supplier, said it would step up security around its oil and gas assets.

“The government has decided to take measures to increase security at infrastructure sites, land terminals and platforms on the Norwegian continental shelf,” said Norway’s Energy Minister Terje Aasland.

The Norwegian Petroleum Safety Authority earlier this week called for “increased vigilance from all operators and shipping companies on the continental shelf”.

Built parallel to the Nord Stream 1 pipeline, Nord Stream 2 should double the capacity for Russian gas imports to Germany.

But Berlin blocked the newly completed Nord Stream 2 in the days leading up to the war.

Germany, which has been heavily dependent on fossil fuel imports from Russia for its energy needs, has since come under acute pressure as Moscow’s supplies dwindle.

Sweden and Poland agree that sabotage is the most likely cause of the Nord Stream leaks, with Warsaw suggesting that Russia was likely the culprit in escalating the war in Ukraine.

The United States said it would investigate the leaks, with Secretary of State Antony Blinken telling reporters that if sabotage was confirmed, “it’s clearly in nobody’s interest.”

The US has pledged to help European allies with energy security and is already shipping what liquefied natural gas it has left over to the EU.