Denmark has joined Sweden in closing its investigation into the 2022 explosions that damaged the Nord Stream gas pipelines, with authorities saying they concluded “there was deliberate sabotage” but “not the sufficient grounds to pursue a criminal case in Denmark”.

Copenhagen police and the Danish security service, who carried out the investigation together, made the remarks in a joint statement.

The Danish authorities said the probe “has been both complex and comprehensive” and Copenhagen police added they were “not able to provide further comments”.

The underwater detonations on the Nord Stream gas pipelines, which were built to carry Russian natural gas to Germany, occurred in international waters but within Swedish and Danish economic zones.

The gas leak in the Baltic Sea
The gas leak in the Baltic Sea (Swedish Coast Guard via AP)

Sweden earlier said that a state actor was the most likely culprit.

Denmark’s investigation was one of three into the explosions.

Sweden spiked its probe on February 7 on the grounds that “Swedish jurisdiction does not apply”, saying the investigation’s primary purpose was to establish whether Sweden or its citizens somehow were involved.

Swedish officials also said they handed over to Germany “material that can be used as evidence in the German investigation”.

Germany still needs to make public its conclusions on the detonations.

The German federal prosecutor’s office said on Monday that the German investigation continues and that it will not provide more information on it for now. It also did not offer a prediction for how long the probe might last.

The source of the explosions has been a major international mystery.

The blasts happened as Europe attempted to wean itself off Russian energy sources following the Kremlin’s full-scale invasion of Ukraine, and contributed to tensions that followed the start of the war.

Nord Stream pipes
The Nord Stream 2 pipeline, which never entered service because Germany suspended its certification process (Michael Sohn/AP)

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 2022.

They also damaged the Nord Stream 2 pipeline, which never entered service because Germany suspended its certification process shortly before Russia invaded Ukraine in February of that year.

The explosions at the pipelines took place about 260 feet underwater on the ocean floor in the Baltic Sea. Seismic measurements indicated that the explosions occurred shortly before the leaks were discovered.

Months after the detonations, 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.

Russia has accused the US of staging the explosions, which they have described as a terror attack. The US has denied involvement.

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.

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.

Swedish prosecutors earlier hinted that the identity of the perpetrator was likely to remain unclear.

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.