French President Emmanuel Macron on Sunday accused Lebanon's leaders of "collective betrayal" over their failure to form a government in the wake of the giant blast at the Beirut port in August.

At a rare news conference devoted to Lebanon, Macron launched an extraordinary diatribe against Lebanese political elite who he said had looked to their own selfish interests rather than those of their country.

"They have decided to betray this commitment (to form a government)," Macron told reporters, declaring he was "ashamed" of the country's leaders.

Macron had repeatedly pressed Lebanon's leaders to form the government, saying a reform-minded cabinet was essential if aid was to flow in to rebuild the country.

Lebanon's premier-designate Mustapha Adib stepped down on Saturday, saying he had been unable to form a government.

"I see that the Lebanese authorities and political forces chose to favour their partisan and individual interests to the detriment of the general interest of the country," Macron added.

Macron said none of the leaders of Lebanon -- where in the wake of the 1975-1990 civil war power is traditionally shared between Shiites, Sunnis and Christians -- had been up to the task.

"All of them bet on the worst case scenario for the sake of saving themselves, the interests of their family or their clan," he seethed.

"I therefore have decided to take note of this collective betrayal and the refusal of Lebanese officials to engage in good faith."

- 'Last chance' -
He also sent a pointed warning to the Iran-backed Shiite group Hezbollah, which was well represented in the outgoing government and some analysts accuse of holding up the process.

Hezbollah should "not think it is more powerful than it is.... It must show that it respects all the Lebanese. And in recent days days, it has clearly shown the opposite," said Macron.

Macron, who visited Lebanon twice in the wake of the explosion, had repeatedly urged the Lebanese not to waste any more time in forming a government.

The August 4 explosion of hundreds of tons of ammonium nitrate at the Beirut port killed more than 190 people, wounded thousands and ravaged large parts of the capital.

The disaster sparked new protests over corruption and mismanagement, prompting the previous cabinet to step down.

The French president said that the roadmap for political and economic reform set out on his last visit on September 1 was still on the table but time was running out.

"It is now up to Lebanese officials to seize this last chance themselves," he said.