Dramatic drone images show devastated Beirut

Aerial footage filmed on Thursday (August 13) showed missing rooftop tiles and windows in the capital city's Hikmeh neighbourhood in Ashrafieh.

Buildings close to the impact area took the full force of the blast, including Saint George's Hospital and electricity supplier Electricite du Liban's headquarters building.

The Aug. 4 explosion, which killed at least 172 people and left much of the capital in ruins, was preceded by a series of six 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 told Reuters on Thursday.

Boaz Hayoun of Israel's Tamar Group, 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.

Causes of these initial blasts are not yet known, but President Michel Aoun has said investigators would also look into the possibility of "external interference" such as a bomb, as well as negligence or an accident as causes.