German prosecutors on Monday opened an investigation into the suspected sabotage of two gas pipelines built to bring Russian gas to Germany under the Baltic Sea.

Undersea explosions late last month ruptured the Nord Stream 1 pipeline, which until Russia cut off supplies at the end of August was its main supply route to Germany. They also damaged the Nord Stream 2 pipeline, which never entered service as Germany suspended its certification process shortly before Russia invaded Ukraine in February.

German federal prosecutors, who investigate national security cases, said they have opened an investigation against persons unknown on suspicion of deliberately causing an explosion and anticonstitutional sabotage.

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Prosecutors said that there is sufficient evidence that the pipelines were damaged by at least two deliberate detonations, and the aim of their investigation is to help identify the perpetrator or perpetrators as well as a possible motive.

The German investigation comes on top of a probe in Sweden. A prosecutor there said last week that evidence had been seized at the site.

The governments of Denmark and Sweden previously said they suspected that several hundred pounds of explosives were involved in carrying out a deliberate act of sabotage. The leaks from Nord Stream 1 and 2 discharged huge amounts of methane into the air.

German federal prosecutors said the reason for them getting involved as well is that an attack on energy supplies could affect Germany's external and domestic security. On Sunday, authorities said that two German boats had set off for the area where the leaks occurred to look into what happened.

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Russian President Vladimir Putin has accused the West of attacking the pipelines, which the United States and its allies vehemently denied.