Lebanon's president Friday rejected any international probe into the catastrophic port blast, saying a missile or negligence could have been responsible as rescuers desperately combed the rubble for survivors. 

The entrenched ruling class has come under fire once again since Tuesday's explosion, which killed at least 154 people and devastated swathes of the capital. 

The revelation that a huge shipment of hazardous ammonium nitrate fertilizer had languished for years in a warehouse in the heart of the capital served as shocking proof to many Lebanese of the rot at the core of their political system. 

Even Lebanese President Michel Aoun admitted Friday that the "paralyzed" system needed to be "reconsidered."

"We are facing changes and reconsidering our system, which is built on consensus, after it was seen to be paralyzed and incapable of swiftly executing decisions," Aoun told reporters. 

He pledged "swift justice" but rejected widespread calls for an international probe, telling a reporter he saw it as an attempt to "dilute the truth."

"There are two possible scenarios for what happened: it was either negligence or foreign interference through a missile or bomb," he said, the first time a top Lebanese official raised the possibility that the port had been attacked. 

What ignited the massive shipment of fertilizer remains unclear – officials said work had recently begun on repairs to the warehouse, while others suspected fireworks stored either in the same place or nearby. 

U.S. President Donald Trump said on Friday that he will join a conference call with Lebanon's president and other world leaders on Sunday to discuss aid to Lebanon. 

Trump said on Twitter that he spoke separately with Lebanese President Michel Aoun and French President Emmanuel Macron, who will also join the call. 

(With input from AFP and Reuters)