Preliminary investigations have “strengthened the suspicions of gross sabotage” behind the crippling of the Nord Stream 1 and 2 gas pipelines, Sweden’s security police said on Thursday.

Swedish and Danish authorities have been investigating four leaks from the gas lines connecting Europe and Russia in the Baltic Sea. The leaks were discovered last week.

After a crime scene investigation, the Security Police can state that there have been detonations at Nord Stream 1 and 2 in the Swedish economic zone, which have caused extensive damage to the gas pipelines, the security police said in a statement.

It added that “certain seizures” were made at the site, and would now be analysed. “The continued preliminary investigation must show whether someone can be served with suspicion and later prosecuted, the security police said.

The blockade around the site has now been lifted, Sweden’s prosecutor’s office said.