Beirut explosion caused by negligence or 'external' missile, Lebanese president said. Lebanese President Michel Aoun says there are two possibilities behind Tuesday’s blast - either negligence or “external intervention” by a missile or a bomb. Aoun said Friday that he asked France for satellite images to see if there were warplanes or missiles in the air at the time of the blast. The blast is believed to have been caused when a fire touched off 2,750 tons of ammonium nitrate stored at the port. The cause of the initial fire is not known. Ref. USAToday.