Security has been increased at all Swedish nuclear power plants after explosives were found close to the Ringhals plant, south of Gothenburg on Wednesday afternoon.

The explosive device was reportedly found on a large truck that had been on the industrial estate belonging to the plant and was returning into the reactor area, which is more heavily guarded.

According to the county police, the device was in the shape of “plastic explosive” and the truck where it was discovered never leaves the plant’s immediate environs.

Maria Stråhle at the Swedish Radiation Safety Authority (Strålsäkerhetsmyndigheten) told TT news agency that “they have all raised the threat level as a precaution.”

The premises was searched over night and no further discoveries were made.

A preliminary investigation is under way and the incident has been classified as a suspected sabotage attempt.