Swedish investigators have discovered traces of explosives at one of the Baltic Sea sites where the Nord Stream 1 subsea pipeline was ruptured, northeast of the Danish island of Bornholm, the country’s Prosecution Authority said in statement released on Friday.

Prosecutor Mats Ljungqvist, who is leading the investigation into the September detonations at Russian gas export pipelines Nord Stream 1 and Nord Stream 2, said that this confirms the incident was “gross sabotage”.

“During the crime scene investigations carried out on site in the Baltic Sea, extensive seizures were made and the area has been carefully documented. Analysis that has now been carried out shows traces of explosives on several of the foreign objects that were found. The analysis work will continue to be able to draw informed conclusions about the incident,” the statement quoted Ljungqvist as saying.

The ongoing investigation, which is being carried out by Swedish and foreign authorities, was described as complex and comprehensive, and aims to determine whether anyone can be served with notice about suspected involvement a criminal act, the statement said.

The Kremlin has been quick to react to the statement, with Russian presidential spokesperson Dmitry Peskov welcoming the findings.

“The very fact that information started to come out in favour of confirming sabotage or a terrorist act, underscores prior Russian statements [on the issue]. It is important not to stop and to find the one behind this explosion,” Peskov said.

At the end of September, subsea explosions, one in the Swedish maritime zone and another one in the Danish maritime zone, damaged two strings of Nord Stream 1 pipeline.

No gas was flowing to Germany at the time, due to Russian gas giant Gazprom’s decision to halt gas supplies to Germany via this route, but the pipeline was still pressurised.

A third explosion is understood to have damaged the first line of Nord Stream 2 system that was also pressurised with natural gas despite remaining idle since last year because of the lack of German operational approvals.

Russian-led surveys

Swiss-registered operator of Nord Stream 1 earlier said that its own survey of the site in the Swedish zone resulted in the discovery of man-made craters on the seabed, where blasts seemed to have completely removed sections of the natural gas pipeline.

However, the operator had also said it would conduct a follow-up subsea survey of the accident site in Danish waters, but has not released any findings from this yet.

Marine traffic services have indicated that the Russian offshore support vessel Nefrit was chartered for these surveys and returned to the Russian Baltic port of Kaliningrad on Thursday.

The Nefrit has not sailed to the site of the Nord Stream 2 explosion, located to the southeast of Bornholm, to continue the Russian survey of the damage to the gas pipelines.

Sweden and Denmark have been maintaining a large exclusion zone around the accident sites in the Baltic Sea since the escape of gas stopped over one month ago.

Operator Nord Stream had not replied to a request from Upstream to confirm the completion of its onsite survey at the time of publication.

The stoppage of Russian gas flows across Nord Stream 1 has apparently weighed heavily on Gazprom, with the company’s total gas exports outside Russia falling by 71.6 billion cubic metres to 93.2 Bcm between 1 January and 15 November this year compared with last year, the gas giant said earlier this week.