Last September the Nord Stream pipelines, which carried billions of dollars worth of Russian gas to Germany via the Baltic Sea, were severely damaged by powerful explosions due to "sabotage."

Russia has accused the U.S. of being responsible for the attack and its European allies of being complicit in an alleged cover-up, a charge Washington says is "complete fiction." But this week U.S. and German intelligence sources suggested Ukrainian or Russian nationals could have been behind the attack.

Here's what we know for certain about the pipeline attacks, what the various parties say about the cause, and some of the key unknowns about an incident that helped accelerate the dramatic decline of Europe's reliance on Russian gas. 

What we know

On September 26, 2022, four Nord Stream 1 and 2 pipelines were damaged by a series of explosions in the Black Sea near Denmark's Bornholm Island, causing large amounts of gas to leak into the water.

Prior to the conflict, the EU imported nearly 50 percent of its natural gas from Russia. Nord Stream 1 had been providing Western Europe with cheap Russian natural gas for more than a decade, accounting for nearly 14 percent of the EU's 2021 gas consumption. 

Germany received more than 50 percent of its annual gas needs via the pipeline. Nord Stream 2, which had been built but was not yet operational, would have dramatically increased that figure, providing enough gas for more than half of Germany's annual consumption. 

Construction of the second gas pipeline was completed in 2021, but Berlin suspended certification for its operations just days before Russia sent its troops into Ukraine. Following the attack, exports via Nord Stream 1 were shut down "indefinitely."

After the explosions, the U.S., EU, NATO and Russia all said the blast was caused by sabotage. In response, Sweden and Denmark, whose exclusive economic zones the attack took place in, launched an investigation with Germany, which six months later has yet to be closed.  

"At this point, it is not possible to say when they will be concluded," a joint letter from the three European countries said in February. "Russian authorities have been informed regarding the ongoing investigations," they added. 

That's despite repeated protests from Moscow, which has launched its own investigation, that the EU nations are not adequately sharing their findings.

"Almost five months have passed since the sabotage of the Nord Stream 1 and Nord Stream 2 gas pipelines. All this time, however, the Swedish authorities, as if on cue, remain silent," Russia's embassy to Sweden said last month. "What is the leadership of Sweden so afraid of?"

Russia has repeatedly called on the 15-member U.N. Security Council to set up an independent inquiry into the blasts, a demand China has supported. However, such a move will need at least nine votes in favor to pass, and most importantly, no vetoes from the Britain, France, the U.S. or China.

What people have said 

Accusations have been flying this week after a New York Times report, citing intelligence reviewed by U.S. officials, said a pro-Ukrainian group may be behind the blasts. 

It stressed there was no evidence that Ukrainian government officials had played any role in the attacks but did say that officials who have reviewed the intelligence "believed the saboteurs were most likely Ukrainian or Russian nationals, or some combination of the two."

A separate report by Germany's ARD broadcaster and Zeit newspaper this week said German authorities had been able to identify the boat used for the sabotage operation. It added a group of six people, using forged passports, had rented the yacht from a Poland-based company owned by Ukrainian citizens, but the nationality of the perpetrators was unclear.

"We have to make a clear distinction whether it was a Ukrainian group, whether it may have happened on Ukrainian orders, or a pro-Ukrainian group (acting) without knowledge of the government. But I am warning against jumping to conclusions," German Defense Minister Boris Pistorius said in response to the reports.

He went on to suggest the attack could also have been a "false flag" operation to blame Ukraine.

Ukrainian Defense Minister Oleksii Reznikov said the media reports were a "little bit strange," stressing the Ukrainian government had "nothing to do" with the attacks. "It's like a compliment for our special forces," he joked. "But this is not our activity."

Russia has seized on the news to once again demand a transparent investigation. Kremlin spokesperson Dmitry Peskov questioned how any U.S. official could assume anything about the attacks without an investigation, suggesting that the reports were a coordinated bid to divert attention from the real culprits. 

U.S. intelligence accused 

Moscow has repeatedly accused the West of being behind the sabotage. "The sanctions were not enough for the Anglo-Saxons: they moved onto sabotage," Russian President Vladimir Putin said following the attacks. "It is hard to believe but it is a fact that they organized the blasts on the Nord Stream international gas pipelines."

Russia's UN Ambassador Vasily Nebenzya told the UN Security Council last month that there was "no doubt about the motive of the crime, nor its perpetrator, nor the way in which the crime was committed." 

He added: "We have strong reasons to doubt the effectiveness, transparency, and impartiality of investigations that are being carried out under some national jurisdictions."

The increased tensions over the pipeline on recent weeks follow the February publication of an article by a Pulitzer prize-winning U.S. journalist who alleged that the U.S., with the help of Norway, was directly responsible for the attack. 

In Seymour Hersh's How America Took Out The Nord Stream Pipeline he claims to have spoken to a source "with direct knowledge" of operational plans by the U.S. security services to use deep-sea divers to damage the pipeline.

Hersch says the source sat in on top-level meetings chaired by National Security Advisor Jake Sullivan and attended by representatives from the president's office, the CIA, and the State and Treasury Departments to deliberate how to destroy the Nord Stream projects as early as 2021.

Hersch alleges the U.S., with the help of NATO ally Norway and the knowledge of Swedish and Danish officials, used the military alliance's BALTOPS 22 drills as cover to plant C4 explosives along the pipelines. The charges, he claims, were detonated three months later via sonar.

The article also suggests that U.S. President Joe Biden had direct knowledge of the planned attack, claiming that was why it could be carried out as an undercover operation without needing to inform U.S. Congress. Biden had said three months before Moscow launched its assault on Ukraine: "If Russia invades... there will be no longer a Nord Stream 2. We will bring an end to it."

At the time of the explosions, U.S. and European officials suggested that Russia may have been responsible for explosions. On the article's release, a White House spokesperson responded by saying the allegations were "false and complete fiction," while a CIA representative said the claims were "completely and utterly false."

Last month, National Security Council spokesperson John Kirby repeatedly denied U.S. involvement saying there was "not a shred" of truth in the article. "The United States, and no proxies of the United States had anything to do with that, nothing."

The 'known unknowns'

Many questions hang over the Nord Stream attacks, the answers to which would have dramatic consequences in the geopolitical sphere. 

If the U.S. were found to be guilty of planning and executing the attack, it could be considered as a direct act of war by one nuclear power against another: Gazprom, which owns a 50 percent stake in the pipelines, is a majority Russian state-owned company. Its profits are thought to have accounted for up to 45 percent of Russia's annual income. 

So why, if the allegations are true, would the U.S. carry out an action that could lead to a direct military standoff with Moscow? 

Hersch, in his article, points to a September 2022 statement from U.S. Secretary of State Antony Blinken: "It's a tremendous opportunity to once and for all remove the dependence on Russian energy and thus to take away from Vladimir Putin the weaponization of energy as a means of advancing his imperial designs."

With the start of the Ukraine conflict and the bombing of the pipelines, Russian gas to the EU has gone from accounting for around 50 percent of the bloc's imports to below 20 percent. That has significantly weakened Europe's reliance and economic ties with its eastern neighbor, bringing it closer to Washington following rocky U.S.-EU relations during Donald Trump's tenure as president.  

Blinken added that the pipeline explosion also "offered tremendous strategic opportunity for the years to come."

That's true for the American energy market, with U.S. Liquid Natural Gas exporters boosting shipments to Europe by more than 137 percent in 2022 compared to 2021. Norway has also seen gains, with its gas export level for 2022 estimated to be 8 percent higher than the year prior.

Another crucial question is why Russia did not respond to the attacks if they were convinced Washington was behind them. Hersh's source reportedly told him: "Maybe they want the capability to do the same things the U.S. did." 

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