STOCKHOLM - Debris collected from the site of the ruptured Nord Stream gas pipelines have revealed evidence of explosives, indicating an act of “gross sabotage,” Swedish prosecutors said Friday, backing up European authorities’ earlier assertions that blasts had deliberately targeted the critical infrastructure.

A series of undersea explosions ripped holes in the Nord Stream pipelines in late September, damaging the links built to carry Russian natural gas to Germany and rendering them unusable. The statement from the Swedish prosecutors provides the first public forensic confirmation that explosives were found at the site.

“Analyses now carried out show residues of explosives on several of the foreign objects found” at the site, said Mats Ljungqvist, the prosecutor in charge of the Swedish investigation.

He did not give further details on the evidence collected or a potential suspect.

Denmark and Germany are also carrying out investigations into the explosions. European authorities have called the leaks “a deliberate act” aimed at exacerbating an energy dispute between Europe and Russia that has escalated since Russian troops invaded Ukraine in February.

Mr Ljungqvist said in a statement that “extensive seizures” had been made and that the area surrounding the sites where the pipes were damaged had been thoroughly documented. Investigators are now carrying out more “advanced analysis,” he said, “with the aim of drawing more reliable conclusions about the incident.”

He described the Swedish investigation as “very complex and extensive” and said that it would continue with the aim of indicating “whether anyone can be suspected of a crime,” without elaborating further.

The two main leaks occurred on each of the pipelines, which consist of a twin strand of pipes, in busy international waters: one northeast and the other south of the Danish island of Bornholm. The Danish authorities said last month that “powerful explosions” had caused the Nord Stream 1 and 2 natural gas pipelines to rupture, although they declined to say who might have caused them.

A submersible drone operator who filmed the site for the Swedish tabloid Expressen after Swedish authorities finished their initial investigation said last month that he could not tell from his images the extent to which Swedish investigators had removed debris from the sea floor, or from the ruptured pipeline itself. The images by the drone operator, Trond Larsen, showed a gaping end of a pipe that appeared to have been sheared off.

Nord Stream AG, the company that owns and operates the Nord Stream 1 pipeline, has said it was allowed to send its own investigative teams to each of the main sites in the waters that fall under Danish and Swedish economic control.

This month, the company said its preliminary survey of the damage site examined by the Swedish prosecutor had shown unnatural craters as deep as 10 to 16 feet and about 800 feet apart. The section of the pipe between the craters was destroyed, and debris had been scattered, Nord Stream said.

Russia has accused the British navy of targeting the pipelines. London has denied any involvement and called the claim a distraction.

Since the blasts, Nato and its European partners have increased patrols around critical infrastructure in the Baltic Sea and the North Sea, which is home to a vast network of cables and pipelines connecting Norway – Europe’s most important energy exporter since Russia invaded Ukraine – to Britain and the European mainland. NYTIMES