French authorities investigating the explosion and fire at LyondellBasell’s storage facility adjoining its refinery at Berre in southern France in the early morning hours of Jul. 14 said their suspicions have been confirmed that the fire was deliberately set.

Prosecutors said they are convinced of “a criminal act, whose motive remains unclear.” The blaze consumed a gasoline and a naphtha storage unit at the site but had no effect on production facilities.

Public prosecutor Dominique Moyal said three potential incendiary devices had been found at the site. Moyal offered no information as to a potential motive nor any details of possible suspects.