Swedish authorities on Friday confirmed that preliminary analytics found traces of explosives on “foreign objects” that were found near the damaged Nord Stream pipelines in what the lead prosecutor described as “gross sabotage.”

Chamber prosecutor Mats Ljungqvist is leading the ongoing investigation into the detonations near the Nord Stream 1 and 2 pipelines that damaged the system in late September. 

The prosecutor confirmed what Western defense officials suspected was an act of sabotage but said the analytics work continues so that investigators can “draw safer conclusions about the incident.”

“The preliminary investigation is very complex and extensive,” Swedish authorities said in a statement. “The continued preliminary investigation must show whether anyone can be served with suspicion of a crime.”

What may have been the largest methane leak in history occurred after four sites along the Nord Stream 1 and Nord Stream 2 pipeline were unexpectedly damaged off the coast of Denmark in the Baltic Sea in late September.

Danish and Swedish authorities have since probed the sites to uncover what happened to the pipelines.  

The pipelines were built to carry natural gas from Russia to Europe and some Western officials were quick to blame Moscow for the attacks, as it has continuously blocked gas supplies to the continent since its invasion of Ukraine and the subsequent fallout with European nations. 

“These are deliberate actions, not an accident,” Danish Prime Minister Mette Frederiksen said on Sept. 27. “The situation is as serious as it gets.”

Russia, who accused the US of using underwater “robots” to target the pipelines, said it would not acknowledge any investigation results if it was not directly involved in the probes.

But Sweden rejected early on any suggestion that Moscow should be involved in the investigations and said “it wasn’t up for discussion.”

“We don’t usually involve foreign powers in our criminal investigations,” Swedish Defense Minister Peter Hultqvist said during an October briefing. “That’s the basic approach. It is not up for discussion.”