Iranian officials say an explosion Wednesday near the southwestern port city of Daylam was caused by construction work, and was not a hostile attack.

News of the blast raised concerns, because it was in the same province where Iran and Russia are building a nuclear reactor. However, the blasting site was about 150 kilometers north of the Bushehr nuclear facility.

Earlier state television reported that residents had seen an aircraft overhead at the time of the blast. The television channel reported that the explosion may have been caused by a fuel tank dropping from an Iranian airplane.