European countries on Tuesday scrambled to investigate unexplained leaks in two Russian gas pipelines running under the Baltic Sea near Sweden and Denmark, infrastructure at the heart of an energy crisis since Russia’s invasion of Ukraine.

Experts and also Russia, which built the network, said the possibility of sabotage could not be ruled out.

Sweden’s Maritime Authority issued a warning about two leaks in the Nord Stream 1 pipeline, shortly after a leak on the nearby Nord Stream 2 pipeline was discovered that had prompted Denmark to restrict shipping within a 5 nautical-mile (9.2 nautical-kilometer) radius.

Both pipelines have been flashpoints in an escalating energy war between European capitals and Moscow that has pummelled major Western economies, sent gas prices soaring and sparked a hunt for alternative energy supplies.

"There are some indications that it is deliberate damage," said a European security source, while adding it was still too early to draw conclusions. "You have to ask: Who would profit?"

Russia also said the leak in the Russian network was cause for concern and sabotage was one possible cause. "No option can be ruled out right now," Kremlin spokesperson Dmitry Peskov told reporters.

Neither pipeline was pumping gas to Europe at the time the leaks were found amid the dispute over the war in Ukraine, but the incidents will scupper any remaining expectations that Europe could receive gas via Nord Stream 1 before winter.

"The destruction that occurred on the same day simultaneously on three strings of the offshore gas pipelines of the Nord Stream system is unprecedented," said network operator Nord Stream AG. "It is not yet possible to estimate the timing of the restoration of the gas transport infrastructure."

Although neither were in operation, both pipelines still contained gas under pressure.

Denmark’s Energy Minister Dan Jorgensen said in a written comment leaking gas had been detected in Nord Stream 2 on Monday between Russia and Denmark.

Russia slashed 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 gas supplies.

The new Nord Stream 2 pipeline had just been completed but had not entered commercial operations. The plan to supply gas via the pipeline was scrapped by Germany days before Russia sent troops into Ukraine in February.

Malfunction or sabotage?

Jakub Godzimirski, a research professor at the Norwegian Institute of Foreign Affairs who specializes in Russian energy policy, said the leaks could have been technical malfunctions but said sabotage was a possibility.

The leaks happened just before the ceremonial launch on Tuesday of the Baltic Pipe carrying gas from Norway to Poland, a centerpiece of Warsaw’s efforts to diversify from Russian supplies.

Norway’s Petroleum Safety Authority (PSA) had urged oil companies on Monday to be vigilant about unidentified drones seen flying near Norwegian offshore oil and gas platforms, warning of possible attacks.

A spokesperson for the Swedish Maritime Administration (SMA) said there were two leaks on Nord Stream 1, one in the Swedish economic zone and another in the Danish zone, adding that both leaks were in an area northeast of the Danish island Bornholm.

"We are keeping extra watch to make sure no ship comes too close to the site," a second SMA spokesperson said.

Vessels could lose buoyancy if they enter the area, and there might be a risk of leaked gas igniting over the water and in the air, the Danish energy agency said, adding there were no security risks associated with the leak outside the exclusion zone.

The leak would only affect the environment locally, which means that only the area where the gas plume in the water column is located would be affected, it said, adding that escaping greenhouse gas methane would have a damaging impact on the climate.

The Danish authorities asked that Denmark’s level of preparedness for the power and gas sector be raised after the leaks, a step that would require heightened safety procedures for power installations and facilities.

"Breaches of gas pipelines happen extremely rarely ... We want to ensure thorough monitoring of Denmark’s critical infrastructure in order to strengthen security of supply in the future," said the head of the Danish energy agency, Kristoffer Bottzauw.