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.