Iranian television is reporting that there has been a large explosion near the southwestern port city of Daylam in Bushehr province.
It was not immediately clear what caused the blast, but residents reported seeing an aircraft overhead.
State television says the explosion may have been caused by a fuel tank dropping from an Iranian airplane.
Iran and Russia are building a nuclear reactor in Bushehr, about 150 kilometers south of where Wednesday's explosion occurred.
Information for this report is provided by Reuters and AP.