The FBI said in a police investigation that the explosion of 500 tons of ammonium nitrate caused the destruction of the port of Beirut and extensive damage in the city last August.
The Lebanese are still holding their political leaders to account, several months after the disaster.
The deadly explosion on August 4 at the port of Beirut was caused by 500 tons of ammonium nitrate, resigned Lebanese Prime Minister Hassan Diab said on Tuesday, citing the results of an investigation by the US Federal Police (FBI).
On the day of the tragedy, which left more than 200 dead and 6,500 injured, Mr. Diab claimed that 2,750 tonnes of ammonium nitrate had been stored for years "without precautionary measures" in a warehouse at the port, blaming the explosion to the presence of this cargo.
However, experts believed that the amount of this high-risk product that caught fire was less.
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The investigation is stalling
While the Lebanese authorities have refused calls for an international investigation, they have allowed French investigators and those of the American FBI to come to Lebanon to participate in the preliminary investigations.
"The FBI report revealed that the quantity exploded was only 500 tons," Hassan Diab said in a meeting with reporters.
But "where did the other 2,200 tonnes go?" He asked.
AFP was unable to verify the contents of the FBI report.
The investigation is still stalling nearly five months after the explosion that traumatized the nation and devastated entire districts of the capital.
Public opinion, angry, is still waiting to know how such a tragedy could have taken place and is demanding that those responsible be held to account.
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Prime Minister indicted
Many leaders, including President Michel Aoun and the Prime Minister, had been officially warned of the danger posed by the presence of ammonium nitrate in the port.
The head of government had presented his resignation a few days after the tragedy, while shirking all responsibility.
But along with three former ministers, Mr. Diab was indicted on December 10 by an examining magistrate.
They are accused of "negligence and causing hundreds of deaths".
A few days later, however, the investigation was temporarily suspended, two ministers accused having called for the disqualification of the examining magistrate Fadi Sawan.
The Court of Cassation must now rule on this request before resuming proceedings.
About 20 people, including port and customs officials, were arrested in connection with the investigation.