Brussels sees signs of "sabotage" and "deliberate" action in the mysterious gas leaks identified on the two Russian-operated Nord Stream pipelines that run under the Baltic Sea.
The infrastructure is at the centre of geopolitical tensions between the EU and Russia, which has been accused of manipulating gas supplies in retaliation for Western sanctions.
The first leak was discovered on Nord Stream 2 on Monday evening around the Danish island of Bornholm. Hours later, two leaks were detected on separate sections of Nord Stream 1, reaching both the Danish and Swedish economic zones of the Baltic Sea.
The cause of the incident remains unclear. An investigation is underway. It might take between one and two weeks for the underwater holes to be inspected, according to Danish authorities.
European Commission President Ursula von der Leyen spoke of "sabotage action" after a call with Danish Prime Minister Mette Frederiksen.
"Paramount to now investigate the incidents, get full clarity on events [and] why," von der Leyen wrote on Twitter on Tuesday evening.
"Any deliberate disruption of active European energy infrastructure is unacceptable [and] will lead to the strongest possible response."
Kadri Simson, European Commissioner for energy, said her team was in contact with member states to "determine the cause and ecological impact of the incidents."
There was no immediate impact on the bloc's energy supplies, Simson noted.
Neither Nord Stream 1 nor Nord Stream 2 were carrying gas to the EU, although some supplies remained inside the 1,200-km infrastructure.
The following day, Josep Borrell, the EU's foreign policy chief, released a short statement on behalf of the 27 member states expressing deep concerns about the unexplained events.
"Safety and environmental concerns are of utmost priority. These incidents are not a coincidence and affect us all," Borrell said on Wednesday morning.
"All available information indicates those leaks are the result of a deliberate act."
The diplomat added the EU would support any investigation aimed at "getting full clarity" around the leaks and take new steps to reinforce the bloc's security of energy supplies.
"Any deliberate disruption of European energy infrastructure is utterly unacceptable and will be met with a robust and united response," Borrell said.
Fears of sabotage began spreading on Tuesday as new details emerged about the Nord Stream gas leaks. The prime ministers of Denmark, Sweden and Poland all raised the possibility of a targeted attack.
The Swedish National Seismic Network said two "probable explosions" had been recorded in the area of the leaks. The first was at 2:03 on Monday, before a second one at 19:03 (CET).
Kremlin spokesperson Dmitri Peskov said blaming Russia was "predictably stupid and absurd."
"This is a big problem for us because, firstly, both lines of Nord Stream 2 are filled with gas," Peskov said on Wednesday. "The entire system is ready to pump gas and the gas is very expensive."
Nord Stream AG, the consortium that operates the twin pipelines, had previously said the damage was "unprecedented" and that it was "impossible" to give an estimation for the recovery.
Images and videos released by the Danish military showed a huge area of gas bubbling on the surface of the Baltic Sea. The largest disturbance had a diameter of more than one kilometre, the military said, while the smallest covered around 200 metres.
The mysterious leaks took place hours before the opening ceremony of the Baltic Pipe, a brand new pipeline that connects Norway with Denmark and Poland. The coincidence further fuelled speculation.
"It is now the clear assessment by authorities that these are deliberate actions," Frederiksen said. "It was not an accident."
EU ambassadors will discuss the issue when they meet on Wednesday, with Germany expected to provide an assessment of the situation.