What we know about the damage to Baltic Sea gas pipelines

Mysterious explosions, methane leaks and giant bubbles of gas in the Baltic Sea — the alleged sabotage of two European pipelines has fuelled anxiety about attacks on infrastructure and a new stage of hybrid war.

Four leaks were detected in the Nord Stream pipelines linking Russia with Germany, all in international waters just off the Danish island of Bornholm in the middle of the Baltic Sea.

Neither pipeline was in operation as supplies in Nord Stream 1 were halted this month by Russia and Nord Stream 2 never came into operation after Germany cancelled its approval process. The leaks coincided with the opening of a new pipeline between Norway, now Europe’s biggest gas supplier, and Poland.

What do we know so far?

The first sign something was up came on Monday morning when German seismologists detected a spike in activity that would coincide with the Nord Stream 2 leak reported later that evening by Denmark.

Seismologists reported a further spike on Monday evening, which probably coincided with the two leaks on the Nord Stream 1 pipeline announced by Sweden’s maritime administration on Tuesday morning. Swedish seismologists said the two powerful spikes in activity were in keeping with explosions, not natural events such as earthquakes. A fourth leak, on the Nord Stream 2 pipeline close to the two leaks on Nord Stream 1, was disclosed by Sweden’s coastguard on Thursday morning.

The leaks occurred in Denmark and Sweden’s exclusive economic zones, not in their territorial waters. Both countries’ prime ministers underscored that as the leaks took place in international waters, there was no attack against either Denmark or Sweden.

The four leaks caused disturbances in the sea up to 1km wide, according to the Danish defence forces. The leaks “risk becoming a climate and ecological disaster”, said Stefano Grassi, head of cabinet for the EU energy commissioner. Denmark said the leaks could have a climate impact equivalent to a third of its annual emissions.

What could have caused the leaks?

The immediate suspicion was that they were acts of sabotage. The Polish and Danish prime ministers both immediately suggested they were unlikely to have been accidents. By Tuesday, Nato had assessed it was sabotage too.

Each steel pipe is about 4cm thick and is coated in up to 11cm of concrete, making each 12-metre section weigh about 24 tonnes, according to the operator of the pipeline, Nord Stream, which is controlled by Russian state gas supplier Gazprom.

The two Nord Stream 1 leaks and one of the Nord Stream 2 leaks are relatively close together and only about 15km from a busy shipping lane. The second Nord Stream 2 leak, however, is about 80km to the south in an even quieter area of sea. There is little passing traffic as it is shielded to the north-west by the island of Bornholm. The leaks are also situated either side of a Danish military firing practice area.

Björn Lund, a member of the Swedish seismic network, told state broadcaster SVT he guessed more than 100kg of dynamite or TNT would be needed to cause such large explosions.

H I Sutton, a submarine expert, wrote on Twitter that the leaks took place in sea with a depth of just 70 metres. He speculated that if Russia was involved in the sabotage it was probably carried out using underwater drones and divers and not submarines. Others argued that a fishing boat or a similar small vessel could have been used.

An energy analyst suggested Russia could have used “malevolent pigs”, referring to the pipeline cleaning and inspecting machines known in the industry as “pigs” used to find faults or clear blockages.

Who could be behind it?

Nato’s secretary-general Jens Stoltenberg cautioned against jumping to conclusions. “This is something that is extremely important to get all the facts on the table, and therefore this is something we’ll look closely into in the coming hours and days,” he said.

Ukrainian officials were quick to point the finger at Moscow. Mykhailo Podolyak, an adviser to Ukraine’s president, said the leaks were “nothing more than a terrorist attack planned by Russia and an act of aggression towards EU”.

Dmitry Peskov, president Vladimir Putin’s spokesman, said on Wednesday that claims of Russia’s involvement were “quite predictably stupid and absurd”, according to Interfax.

Radek Sikorski, a former Polish foreign minister, suggested the leaks were the result of US sabotage, posting a picture of one of the leaks with the words: “Thank you, USA”. The US administration was critical of Nord Stream 2 which, before it was frozen shortly before Moscow’s full-scale invasion of Ukraine in February, would have been used to bypass Ukraine.

Maria Zakharova, Russia’s foreign ministry spokesperson, said on Thursday that the Nord Stream incident “happened in the waters of countries under the complete control of American secret services”, according to state newswire Tass.

US national security adviser Jake Sullivan said in a tweet on Wednesday that he had spoken to his Danish counterpart “about the apparent sabotage” adding: “The US is supporting efforts to investigate and we will continue our work to safeguard Europe’s energy security.”

What comes next?

Concern has mounted in western intelligence circles in recent years that Russia has been testing the vulnerability of critical infrastructure in some countries.

One of the two fibre optic cables linking the Norwegian mainland with the Arctic archipelago of Svalbard was cut in January, with police blaming human activity. Norway also warned on Monday that unidentified drones had been flying close to several oil and gas rigs over several months, prompting investigations by police and intelligence services.

Russian security services last week claimed they had thwarted a planned Ukrainian attack on the TurkStream pipeline that supplies Turkey and parts of southern Europe. Kyiv rejected the allegations. A western security source suggested that the Russian allegation would be consistent with other suspected “false flag” operations by Moscow to spread doubt and suspicion about who was behind any subsequent attacks.

Analysts said the worst-case scenario for Europe would be sabotage of an active pipeline such as one between Norway and the continent or the UK. Oslo on Tuesday night raised the preparedness level of its oil and gas installations amid widespread concern in Norway.

Additional reporting by David Sheppard and John Paul Rathbone in London and Henry Foy in Brussels