COPENHAGEN, Denmark (AP) — Swedish officials said Wednesday that they have decided to close their investigation into the September 2022 explosions on the underwater Nord Stream gas pipelines which were built to carry Russian natural gas to Germany, saying they don’t have jurisdiction.

Sweden's investigation was only one of three into the explosions. Denmark and Germany are also examining the blasts.

The attack, which happened as Europe attempted to wean itself off Russian energy sources following the Kremlin’s full-scale invasion of Ukraine, contributed to tensions that followed the start of the war. The source of the sabotage has been a major international mystery.

Public prosecutor Mats Ljungqvist from the Swedish Prosecution Authority said in a statement that "Swedish jurisdiction does not apply.”

The probe's primary purpose was “to establish whether Swedish citizens were involved” and whether Sweden somehow was used to carry out the detonations, thereby putting the Scandinavian country at risk, the authority said.

Hans Liwång of the Sweden Defense University called it “a natural decision.”

“Already from the beginning, they said that it’s not necessarily the case that this is a crime performed toward Sweden,” Liwång said. The probe “was a fact-finding and evidence-finding process (and) that it may be dropped when they’ve gathered enough information to know what had happened and how.”

The undersea explosions ruptured the Nord Stream 1 pipeline, which was Russia’s main natural gas supply route to Germany until Russia cut off supplies at the end of August that year.

The blasts also damaged the Nord Stream 2 pipeline, which never entered service because Germany suspended its certification process shortly before Russia invaded Ukraine in February 2022.

Kenneth Øhlenschlæger Buhl of the Royal Danish Defense College said the Swedish decision ”indicates there could have been some kind of a political involvement.”

“There might be a good reason for not going out with a conclusion,” Øhlenschlæger Buhl said. “Sweden stands in a sensitive position as it wants to join NATO and may not want to rock the boat further.”

After Russia invaded Ukraine, Sweden set aside decades of military nonalignment to seek protection under NATO’s collective defense umbrella.

All NATO members must give their approval for new countries to join the grouping, and Hungary is the only member that hasn’t done so for Sweden. Its prime minister, Viktor Orbán, has been accused by critics of promoting Moscow’s interests over those of his EU and NATO allies.

The explosions at the pipelines took place about 80 meters (260 feet) underwater on the ocean floor in the Baltic Sea in the Swedish and Danish economic zones but in international waters. Seismic measurements indicated that the explosions occurred shortly before the leaks were discovered.

Ljungqvist, who declined to comment further on the Swedish investigation, said Swedes had “in-depth cooperation" with Germany and have "been able to hand over material that can be used as evidence in the German investigation.”

In Germany, federal prosecutors said “our investigations are continuing,” declining to comment further.

Copenhagen police, which are leading the Danish investigation, said their probe “is still not finally finished” and that an announcement is expected "within a short time.”

Beyond their geopolitical impact, the Nord Stream pipeline leaks were a huge environmental disaster with local wildlife affected and huge volumes of methane discharged into the Baltic Sea in what analysts believe could be the single largest release of methane due to human activity.

More than 16 months after the sabotage there is no accepted explanation. A series of unconfirmed reports variously accusing Russia, the United States and Ukraine are filling an information vacuum as investigations into the blasts continue.

The pipelines were long a target of criticism by the United States and some of its allies, who warned that they posed a risk to Europe’s energy security by increasing dependence on Russian gas.

Russian President Vladimir Putin and Russian officials have accused the U.S. of staging the explosions, which they have described as a terror attack. The U.S. has denied involvement.

In Moscow, Putin’s spokesperson, Dmitry Peskov, called the Swedish decision “remarkable.”

“Of course, now we will need to see how Germany itself reacts to this. After all, this is a country that lost a lot in connection with this terrorist attack, gave up a lot in connection with this terrorist attack,” Peskov told reporters.

"It will be interesting how scrupulously the German authorities will approach this investigation,” he said.

In March 2023, German media reported that a pro-Ukraine group was involved in the sabotage using a vessel and setting off from the German port of Rostock. Ukraine rejected suggestions it might have ordered the attack and German officials voiced caution over the accusation.

The German and Danish investigations have yet to shed light on the incident and while Swedish prosecutors have said that a state actor was the most likely culprit, they cautioned that the identity of the perpetrator was still unclear and hinted that it was likely to remain so.

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Associated Press writers Geir Moulson in Berlin and David Keyton in Stockholm contributed to this report.

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This story has been corrected to show that NATO members must approve new members, not EU members.