Swedish seismologists detected explosions underneath the Baltic Sea on 26 September. It was later discovered that methane was leaking from the Nord Stream 1 and 2 pipelines, which were constructed to deliver Russian natural gas to Germany. Both lines of NS 1 and one line of NS 2 are heavily damaged and potentially unusable forever.

It is suspected that the leaks were caused by sabotage. Poland and Denmark quickly suggested that the leaks were unlikely to have been accidents. It takes effort to damage the Gazprom pipelines: Nord Stream 1 has a roughly 3cm thick steel wall and is coated in about 10cm of concrete.

Although the perpetrator of the suspected sabotage acts has not been confirmed, Russia is the main suspect. As a result, given that the alleged acts were carried out within the exclusive economic zones of EU and NATO countries, the Union and the Alliance have reacted strongly.