Investigators have found traces of explosives at the site of the damaged Nord Stream pipelines, confirming that gross sabotage had taken place, a Swedish prosecutor said on Friday.
Swedish and Danish authorities are investigating four holes in the Nord Stream 1 and 2 pipelines which link Russia and Germany via the Baltic Sea and have become a flashpoint in the Ukraine crisis.
Denmark last month said a preliminary investigation had shown that the leaks were caused by powerful explosions.
"Analysis that has now been carried out shows traces of explosives on several of the objects that were recovered," the Swedish Prosecution Authority said in a statement.
"The investigation is highly complex and comprehensive. The ongoing probe will determine whether any suspects can be identified," it added.
The prosecutor's office declined to give further comment, according to Reuters.
Seismologists in Denmark and Sweden have previously said they had registered tremors in the immediate vicinity of the leaks and that the signals did not resemble those from earthquakes.
The Sept 26 ruptures of the seabed pipelines, spewing gas into the ocean that bubbled to the surface in the week that followed, triggered warnings of public hazard and fears of environmental damage.
A section measuring at least 50 metres (164 feet) is missing from Nord Stream 1, Swedish daily Expressen reported on Oct 18 after filming what it said were the first publicly released images of the damage.
Russia's defence ministry last month said that British navy personnel blew up the pipelines, a claim that London said was false and designed to distract from Russian military failures in Ukraine.