Swedish investigators said Friday they found explosive residue at the site of mysterious blasts that hit the Nord Stream pipelines and concluded that the leaks were caused by "gross sabotage."

The big picture: Four ruptures were discovered in the Nord Stream 1 and 2 pipelines at the end of September, causing leaks in the exclusive economic zones of Sweden and Denmark that created extensive environmental damage.

• Western officials previously indicated that the explosion was a result of sabotage.
• Russia has denied responsibility for the blasts and claimed they were an act of "international terrorism."

Why it matters: The pipelines are designed to send Russian gas to the European Union and have become a flashpoint since the invasion of Ukraine.

• Denmark and Sweden said in September that the blasts "probably corresponded to an explosive load of several hundred kilos."

What they're saying: "In the crime scene investigations carried out on site in the Baltic Sea, the area and the extensive damage to the gas lines as a result of the detonations have been extensively documented," the Swedish Prosecution Authority said in a statement.

• "During analyzes carried out, residues of explosives have been identified on several of the foreign objects seized," it said.