On Monday, seismologists in Denmark and Sweden recorded strong explosions in the areas where three gas leaks from the Nord Stream 1 and 2 gas pipelines connecting Russia to Germany via the Baltic Sea were later reported, the Swedish National Seismological Center (SNSN) announced on Tuesday, Reuters and AFP report.

“Without a doubt these were explosions,” Swedish seismologist Bjorn Lund told SVT.

A seismograph on the Danish island of Bornholm recorded movements that represent earthquakes twice on Monday.

A first “massive energy release” of magnitude 1.9 was recorded overnight Sunday into Monday at 00:03 GMT southeast of the island of Bornholm, then another of magnitude 2.3 at at 17:04 GMT on Monday evening, north of the same island, states the quoted seismologist, according to Agerpres.

The three large gas leaks are currently visible from the surface of the water, causing bubbles with diameters between 200 meters and one kilometer, according to images from the scene released by the Danish military.

Gas deliveries through the Nord Stream 1 pipeline were stopped by Russia this month, and the new Nord Stream 2 gas pipeline was not put into operation following the European sanctions imposed on Russia after the aggression against Ukraine. Although taken out of service, the two pipelines remained full of gas.

The three gas leaks seem to indicate sabotage rather than an accident, but it is not clear who and why would have resorted to such an action.