The Beirut port explosion was preceded by a series of blasts, the last of which was a combustion of fireworks that apparently set off a warehouse full of ammonium nitrate, an Israeli seismological and munitions expert said on Thursday.
Boaz Hayoun, a former Israeli military engineering officer whose current roles include overseeing safety standards for explosives use in Israel, said the six preliminary blasts were tracked by a seismological sensor array installed some 70 km (43 miles) off Lebanon's coast by the international geological project IRIS.
"I cannot say categorically what caused this, but I can say these blasts were at the same location," Hayoun told Reuters.