COPENHAGEN, Denmark — (AP) — Sweden’s domestic security agency said Thursday its preliminary investigation into leaks from two Russian gas pipelines in the Baltic Sea “has strengthened suspicions of serious sabotage” as a cause, and a prosecutor said evidence at the scene has been seized.

The Swedish security service said the probe confirmed that “detonations” caused extensive damage to the Nord Stream 1 and Nord Stream 2 pipelines. Authorities had said when the leaks outside Sweden and Denmark first emerged that explosions were being recorded in the area.

The agency, which said what happened in the Baltic Sea was “very serious,” gave no details of its investigation.

But in a separate statement, Swedish prosecutor Mats Ljungqvist says that “seizures have been made at the crime scene and these will now be investigated.”

Ljungqvist, who led the preliminary investigation, has not identified the seized evidence. Ljungqvist said he had given “directives to temporarily block (the area) and conduct a crime scene investigation.”

Now that the first sounding is complete, a blockade around the pipelines outside Sweden will be lifted, he said.

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

Last week, underwater explosions ruptured Nord Stream 2 and its sister pipeline, Nord Stream 2, at two locations off Sweden and two off Denmark. The pipelines were built to transport Russian natural gas to Germany.

Danish authorities said the two methane leaks they were monitoring in international waters stopped over the weekend. One of the leaks outside Sweden also appeared to have stopped.

Russian President Vladimir Putin accused the West of attacking the pipelines, which the US and its allies have strongly denied, noting that Russia has the most to gain from disrupting Europe’s energy markets.

Separately, the Swedish Coast Guard said that “remaining emissions are more or less unchanged” and that they are returning to their regular environmental rescue operations.

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