European authorities are preparing to start investigating a series of incidents that left three out of four strings of Russian Nord Stream 1 & 2 projects inoperable, and they expect the remaining gas could escape from the 1200-kilometre subsea pipelines by 2 October.

More than half of the gas in the damaged pipelines has leaked out of the pipes in the Swedish and Danish economic zones of the Baltic Sea and the remaining volume is expected to be gone by Sunday, the head of the Danish Energy Agency, Kristoffer Bottzauw, said on Wednesday, according to Reuters.

Though both projects were idle at the time of the pressure-drop incidents on Monday, each string is thought to have held more than 170 million cubic metres of natural gas under pressure to permit a quick resumption of pumping when needed.

The magnitude of the incident has been underscored by another video released by the Swedish coast guard on Wednesday, confirming earlier estimates of the size of the gas leaks on the Baltic sea surface of up to about one kilometre in diameter.

Not a coincidence

European Union officials have expressed strong concerns, with High Representative of the European Union for Foreign Affairs and Security Policy Josep Borrell saying in a statement that “these incidents are not a coincidence and affect us all”.

“Safety and environmental concerns are of utmost priority,” Borrell said, apparently referring to the volume of gas that will escape into the Earth’s atmosphere.

Over a 20-year period, methane is estimated to be 80 times more potent at warming than carbon dioxide, according to the United Nations Environmental Programme.

“All available information indicates those leaks are the result of a deliberate act. We will support any investigation aimed at getting full clarity on what happened and why, and will take further steps to increase our resilience in energy security,” Borrell said.

“Any deliberate disruption of European energy infrastructure is utterly unacceptable and will be met with a robust and united response,” he said.

Nord Stream incidents have been described in some statements in the West as sabotage, though without attempting to name who was involved.

Nato's Secretary General Jens Stoltenberg tweeted on Wednesday that he had discussed "the sabotage" on the pipelines and the protection of critical infrastructure with Danish Defence Minister Morten Bodskov.

According to a partner in Moscow-based energy consultancy RusEnergy, Mikhail Krutikhin, Gazprom is seen in a winning position after these incidents as the Russian gas giant may declare a force majeure – an unexpected event that prevents someone from meeting obligations in a legal agreement – on its long-term gas supply contracts with European customers and argue for relief from possible arbitration appeals over its refusal to supply gas via Nord Stream 1.

New sanctions on table

The incidents are also understood to have added urgency for the ongoing European discussion about agreeing a new package of restrictive measures against Russia in response to its military aggression in Ukraine and controversial referenda in occupied territories.

European Commission President Ursula von der Leyen on Wednesday said in a statement that the proposed package of sanctions will “isolate and hit Russia's economy even more”.

“We propose sweeping new import bans on Russian products. This will keep Russian products out of the European market and deprive Russia of an additional 7 billion euros in revenues,” she said.

“We are also proposing to extend the list of products that cannot be exported to Russia anymore... to deprive the Kremlin's military complex of key technologies,” Von der Leyen said.

She suggested the new export bans would further weaken Russia's economy and its ability to modernise.

The European Commission also will propose bans on offering European services to Russia and prohibiting EU nationals from sitting on governing bodies of Russia's state-owned enterprises, she said.