BERLIN (AP) — German officials say they are investigating whether the deaths of 18 porpoises in the Baltic Sea is connected to a navy demining operation earlier this year.

A spokesman for Germany’s Defense Ministry said Monday that “so far no direct link has been established” between the detonation of 42 WWII-era mines and the deaths of the endangered marine mammals.

Frank Faehnrich told reporters that should a link be found “we obviously regret it.”

The mines were blown up in August during a NATO maneuver, after civilian authorities warned they were becoming increasingly unsafe with age.

Environment Ministry spokesman Stephan Gabriel Haufe said the detonation took place in a marine reserve and that porpoises in the Baltic enjoy “particularly strict protection.”