A preliminary investigation into leaks from two Russian Nord Stream pipelines in the Baltic Sea has strengthened suspicions of serious sabotage. Sweden's internal security agency said this, Reuters reported.

According to it, the investigation confirmed that the Nord Stream 1 and Nord Stream 2 pipelines suffered significant damage last week as a result of a detonation.

The agency did not give details of its investigation, but in a separate statement, Swedish prosecutor Mats Ljungqvist said that seizures were made at the scene.

He did not specify what evidence was involved, but said that now that the initial investigation is complete, the cordon around the pipelines off the Swedish coast will be lifted.

Ljungqvist called it a serious incident, noting that the case is very sensitive. He declined to go into detail, citing pre-trial confidentiality.