Lebanese Prime Minister Hassan Diab said that an estimated 2,750 tons of ammonium nitrate had been stored at a warehouse in Beirut for six years, according to a statement published on the Republic of Lebanon Presidency website.
Ammonium nitrate is a key ingredient in both fertilizer and certain types of explosives. The substance has been used in terror attacks, including the bombing of the Alfred P. Murrah Federal Building in Oklahoma City in 1995.
It's still unclear what exactly caused the Tuesday explosion in Beirut that killed nearly 80 people. The blast was earlier blamed on a fire that broke out.
Lebanon's General Security Chief Abbas Ibrahim said earlier "highly explosive material" that had been confiscated years ago was being stored in the warehouse, which is just minutes' walk from popular shopping and nightlife districts.
Prime Minister Diab said in the statement it was "unacceptable" that so much explosive material was stored in a warehouse "without taking preventive measures while endangering the safety of citizens."
"I will not rest until we find those responsible for what happened, hold them accountable, and impose maximum punishment," he said.
Diab gave his condolences and wished for the speedy recovery of the wounded. He called for the formation of an investigation committee into the cause of the blast, which should release its results within a maximum of five days, added the statement.