Last week, two gas lines carrying Russian gas to Europe were reported damaged, with sabotage being the primary cause. Two underwater explosions were reported near the contentious Nord Stream 1 and 2 gas pipelines, and a Danish F-16 fighter jet confirmed evidence of a massive natural gas leak into the Baltic Sea. The Danish Energy Agency announced on Sunday that the leaks had been stopped.

The incident began on September 26 when Nord Stream 2 pipeline operators noticed a sudden drop in pressure from 105 to just 7 bars. The Nord Stream 2 pipeline, despite being completed and partially filled with gas, was never operational. When Russia invaded Ukraine earlier this year, Germany, the pipeline’s landfall and the primary intended recipient for the gas, halted its imminent activation.

Nord Stream 1, which is operational but being throttled by the Russian government due to NATO support for Ukraine, also registered a pressure drop.

Along with the two pressure drops, two explosions were recorded by seismic monitoring stations in Sweden and Denmark. According to a Swedish National Seismic Network expert, the explosions were set off underwater because the data showed shock waves bouncing off the ocean floor and then refracting upward. Each occurred near one of the two pipelines and had the magnitude of a 2.3-scale earthquake. According to Denmark and Sweden in a letter to the United Nations Security Council, the explosions likely correspond to “an explosive load of several hundred kilos.”

Both pipelines begin in Russia, transporting natural gas from the Bovanenkovo gas field in western Siberia to Germany via the Baltic Sea. The pipelines enter the territorial waters of Russia, Germany, and Denmark in the Baltic. They also pass-through Russia’s, Finland’s, Sweden’s, Denmark’s, and Germany’s Exclusive Economic Zones (EEZs). EEZs differ from territorial waters in that the country claiming an EEZ has first claim to economic development in that zone, but it cannot legally bar foreign ships, including warships, from using it.

According to Reuters, Germany’s Economy Minister stated that the leaks were the result of targeted attacks on infrastructure and ruled out an engineering or material flaw. The governments of Sweden and Denmark believe the leaks were the result of deliberate action, possibly sabotage. President Joe Biden also called the attacks a “deliberate act of sabotage” on Friday. According to Germany’s Spiegel news magazine, the US Central Intelligence Agency warned Berlin this summer of possible attacks on natural gas pipelines.

Russia was immediately identified as a perpetrator—it has used its economic leverage as a natural gas supplier to the rest of Europe. Recently, Moscow cut the supply of gas to Nord Stream 1 for “maintenance,” reducing the amount of gas sent by 40%.

These moves are widely interpreted as retaliation against NATO countries such as Germany and Denmark, which have provided arms and other assistance to Ukraine. One possible motivation would be to put pressure on NATO countries, which are bracing for a harsh winter, to stop sending aid to Ukraine; Russia could gain additional concessions by agreeing to repair the damaged lines.

Undersea warfare expert HI Sutton notes on Twitter that the Soviet Union had a significant underwater spy capability during the Cold War, which Russia inherited. Russia has continued that tradition with midget submarines and spy submarines like the Belgorod, but Sutton believes these could not have been involved in the incident.

Russia’s war in Ukraine has not gone well, forcing it to resort to increasingly desperate measures, such as mobilizing tens of thousands of poorly trained civilians to levy depleted forces in Ukraine. NATO’s assistance to Ukraine has been spectacularly effective, particularly in the areas of anti-tank missiles, artillery, and anti-ship missiles. To have a chance of winning, Russia must end NATO military support for Ukraine, but it cannot take on NATO militarily.