Seismologists record two "massive releases of energy" shortly before leaks in the Russia-Europe gas pipelines, with the EU foreign policy chief pointing to "a deliberate act".
Sabotage is the most likely cause of leaks in two Baltic Sea gas pipelines between Russia and Europe, European leaders have said, after seismologists reported explosions around the Nord Stream pipelines.
The EU considers the leaks "are not a coincidence", with indications they were "a deliberate act", the bloc's foreign policy chief Josep Borrell said on Wednesday, calling for an investigation.
"Any deliberate disruption of European energy infrastructure is utterly unacceptable and will be met with a robust and united response," he warned in a statement, a day after EU chief Ursula Von der Leyen too said "sabotage" caused the leaks.
The Nord Stream 1 and 2 pipelines have been at the centre of geopolitical tensions in recent months as Russia cut gas supplies to Europe in suspected retaliation against Western sanctions following its military offensive against Ukraine.
Danish Prime Minister Mette Frederiksen pointed to "deliberate acts", saying: "We are not talking about an accident". Polish Prime Minister Mateusz Morawiecki said the leaks were an act of sabotage that "probably marks the next step of escalation of the situation in Ukraine".
And Sweden's outgoing Prime Minister Magdalena Andersson said "there have been detonations", although Foreign Minister Ann Linde said they would not "speculate on motives or actors".
Copenhagen expects the leaks at the pipelines, which are full of gas but not operational, to last "at least a week" — until the methane escaping from the underwater pipes run out.
Like Denmark, the Swedish government said it does not consider this as an act of aggression against it, given that the events took place outside its territorial waters, in the exclusive economic zones.
Two "massive releases of energy" were recorded by the Swedish National Seismic Network shortly before the gas leaks near their locations off the coast of the Danish island of Bornholm, Uppsala University seismologist Peter Schmidt told AFP news agency.
"With energy releases this big there isn't much else than a blast that could cause it," he added.
Russia said earlier that it was "extremely concerned" about the leaks.
Asked by reporters whether it could be an act of sabotage, Kremlin spokesperson Dmitry Peskov said that at the moment "it is impossible to exclude any options".
But Ukraine said it was "nothing more than a terrorist attack planned by Russia and an act of aggression towards the EU".
The pipelines are operated by a consortium majority-owned by Russian gas firm Gazprom.
One of the leaks on Nord Stream 1 occurred in the Danish economic zone and the other in the Swedish economic zone, while the Nord Stream 2 leak was in the Danish economic zone.
A leak was first reported on Nord Stream 2 on Monday.
Two Danish military vessels have been dispatched to the area, while Sweden's government called an emergency meeting on Tuesday.
Navigational warnings have been issued for a distance of five nautical miles and a flight height of 1,000 metres (3,280 feet) around the Baltic Sea leaks.
"Gas pipeline leaks are extremely rare and we therefore see a reason to increase the level of preparedness following the incidents we have witnessed over the past 24 hours," Danish Energy Agency director Kristoffer Bottzauw said in a statement.
A Nord Stream spokesperson told AFP news agency they had not been able to assess the damage but conceded that "an incident where three pipes experience difficulties at the same time on the same day is not common".
Built in parallel to the Nord Stream 1 pipeline, Nord Stream 2 was intended to double the capacity for Russian gas imports to Germany. But Berlin blocked newly completed Nord Stream 2 in the days before the Ukraine conflict erupted.