HAMBURG, Germany — A former Ukrainian army officer goes on trial in Germany on Wednesday over undersea explosions that damaged the Nord Stream gas pipelines linking Russia and Germany four years ago in what is considered one of Europe’s biggest acts of sabotage since World War II.

The suspect faces charges of causing an explosion, damaging property, disrupting public service and being an “accomplice to war crimes” by attacking civilian infrastructure, according to prosecutors.

According to German privacy rules, the suspect will be identified in court only as Serhii K., although he was publicly named as Serhii Kuznietsov in extradition proceedings in Italy.

While international observers initially blamed Moscow, investigators have increasingly examined suggestions that Ukrainian state security agencies may have been involved — even though Ukraine counts Germany as one of its closest allies.

The trial of the suspect, who is believed to be the alleged ringleader of the attack, is being held under strict security measures at the Hanseatic Higher Regional Court in Hamburg.

According to the charges, the defendant was allegedly involved in causing the Sept. 26, 2022, explosions that damaged pipelines built to carry Russian natural gas to Germany under the Baltic Sea.

At the time, European countries were moving to wean themselves off Russian energy sources, following the Kremlin’s full-scale invasion of Ukraine in February 2022.

Prosecutors say the aim of the plot was to permanently disrupt gas deliveries and prevent Russia from using the revenues to finance its military operations.

The defendant and others allegedly used a yacht that departed from the German port of Rostock. It had been rented from a German company using forged IDs and with the help of intermediaries.

The explosions ruptured the Nord Stream 1 pipeline, which was Russia’s main natural gas supply route to Germany until Moscow cut off supplies in August 2022. They also damaged Nord Stream 2, which never entered service because Germany suspended its certification process shortly before Russia’s invasion of Ukraine.

The suspect allegedly organized and carried out the detonation of at least four bombs between 14 and 27 kilograms (around 31 to 62 pounds) at a depth of 70 to 80 meters (230 feet to 263 feet) near the Danish island of Bornholm.

He was detained in 2025 in an Italian village, where officers raided a bungalow where he was staying with his family. Police said he surrendered without resistance. He was extradited to Germany in November.

A second suspect was arrested on a European warrant in the northern Croatian town of Pula in August. He has applied for asylum in Croatia to fight his extradition to Germany.

The pipelines were long a target of criticism by the U.S. and some of its allies, which warned that they increased dependence on Russian gas.

Russia has claimed that U.S. and British intelligence agencies were involved in staging the explosions and has also accused NATO of involvement in the attack, while several Western countries initially blamed Russia.

Ukrainian President Volodymyr Zelenskyy has denied allegations that his country was involved in the pipeline blasts.

The German government has so far refrained from comment on the upcoming trial, pointing out that no verdict has yet been reached and the case is in the hands of the independent judiciary.

So far, 16 court dates have been scheduled through Dec. 17. Additional dates are also planned for January and February 2027. It is not yet known when the verdict will be announced.