"Hariri's resignation was done with planning by Donald Trump, the president of America, and Mohammed bin Salman, the crown prince of Saudi Arabia", said Hussein Sheikh al-Islam, adviser to Iran's supreme leader.
The ostensible reason he gave, as he invoked his late father's name, was that he too is threatened with assassination.
Hariri allies in Lebanon have denied suggestions he had been detained and a photograph was published on his Twitter account showing him with Saudi Arabia's newly appointed ambassador to Lebanon, Walid al-Yaaqoub.
He was also seen as giving in to Hezbollah interests on budgetary issues.
Hariri's resignation was widely seen as a Saudi move against Hezbollah, the Shiite political group and guerrilla force that is Iran's powerful arm in Lebanon and Syria.More news: Plane-sized 'void' discovered in Egypt's Great Pyramid
"We do not want explosions and destruction to happen again in the Hariri family", he added, referring to the fatal bombing of Saad al-Hariri's father and prime minister of Lebanon, Rafik Hariri, in 2005. His actions have already all but destroyed the Gulf Cooperation Council (GCC); Yemen can no longer be referred to as a functioning state; Egypt is a ticking time bomb; and now Lebanon may erupt. Nasrallah said Lebanon's political leaders expected Hariri to return to Lebanon on Thursday "if he is allowed" to travel.
The main significance of Nasrallah and President Aoun's remarks is that the Lebanese government is not disintegrating in light of the announcement of Hariri's resignation. "They hope a chaotic situation and difficulties assembling a government will limit Hezbollah's ability to maneuver and to achieve its objectives".
The government was formed late last year in a political deal that ended years of deadlock, and last month it produced Lebanon's first budget since 2005.
Since taking office, Hariri had worked to garner international aid for Lebanon to cope with the strain of hosting some 1.5 million Syrian refugees, seeking billions of dollars to boost its sluggish economy.
Saudi-owned newspaper Asharq al-Awsat cited unnamed sources close to Hariri as speculating that he would probably remain outside Lebanon because of the security threat against him.
Mr Hariri has been prime minister since December 2016, after previously holding the position between 2009 and 2011. Yemen's fate is still being battled out.