Hariri returned to Saudi Arabia after a short visit to Abu Dhabi on Tuesday.
On 4 November, while in Riyadh, Hariri announced his resignation, citing fears for his life.
In 2004, Hariri's father was allegedly killed by Hezbollah, the Shia-Muslim, Iran-backed group that dominates political life in Lebanon.
“Mr Hariri has resigned in Saudi Arabia,” says Farid El-Khazen, a politician close to President Michel Aoun. “The president of Lebanon is waiting for him to come to Lebanon to discuss the issue so that a decision can be made regarding the next step, to form a new government.
"The logical step would be for Hariri to come to Lebanon and to discuss the issue or to present his resignation in Lebanon.”
It is unclear what effect Hariri’s resignation will have on his country, which has a complex system called “sectarian democracy”, with over 100 political parties gathered in two large coalitions.
Under that system, Hariri was appointed prime minister at the end of 2016.
“Lebanon has been functioning for a while with the concept that there is no winner and no loser,” says Rania Masri, a researcher at Balamand Univesity. This balance may now be lost."
Hariri has dual Saudi-Lebanese citizenship and, according to Masri, business dealings with some Saudi princes, and she believes he is tied to the regime in Riyadh.
“We know very clearly that the Saudi government is planning something bad for Lebanon," she comments.
“Will it be a financial blockade? Will it be financial destruction? Will it be the creation of an Isis-like terrorist cell in Lebanon as they created in Syria? We don’t know. Will it simply be that they impose on us their more loyal prime minister, that Saad Hariri, was and then he will seek to dismantle the unified ministry that we have?"
Big changes in Saudi
Just hours after Hariri's announcement, a political storm broke in Saudi Arabia itself.
The official Saudi Press Agency issued a series of four statements announcing the resignation and replacement of some of the kingdom's key ministers and military officers, as well as the creation of a Committee on Corruption.
Some of the people detained were put under house arrest in the Ritz-Carlton hotel. According to Bloomberg, among those affected are four of Saudi Arabia’s richest people, including the late King Abdullah's nephew Alwaleed bin Talal, who is worth 19 billion dollars (16 billion euros); Saleh Kamel, worth 3.7 billion dollars (3.2 billion euros), who made his millions by running bus services for Hajj pilgrims, and Bakr Bin Laden, the brother of Osama Bin Laden and head of one of Saudi Arabia’s biggest construction groups.
The purge has caused a lot of speculation.
Saudi Arabia’s most famous tweeter, @mujtahidd, who has a massive 1,9 million followers, added fuel to the fire with a series of tweets, making startling allegations that linked the visit of US President Donald Trump to the rise of Saudi Crown Prince Mohamed bin Salman, who has become the real power in the land.
Others reject the tweets as pure speculation.
“I’d be cautious in saying that Trump played a role,” says Gerald Steinberg, a political scientist with Bar Ilan University. “The new crown prince is young and the issue of Iran is extremely essential to him.”
Mohammed Bin Salman sees “the threat from Iran and its moves with respect to Hezbollah and Lebanon and their threats there, and the Iranian presence in Yemen as the same force,” says Steinberg, and he would have reached his conclusions about Iran regardless of Trump. “But one has to assume that having American support makes him act more boldly."
Meanwhile, others don’t see the arrests as a political purge, aimed at strengthening “MBS's” position but merely proof that he is following up on promises of reform, more freedoms for women, such as September's law allowing women to drive cars and the announcement that women can now attend football matches.
“What is happening here is that there is a prince that is very determined to raise a new Saudi Arabia and one pillar of the new Saudi Arabia is zero-tolerance to corruption,” says professor Abdulkhaleq Abdullah, of the United Arab Emirates University.
“I think we are in for a new Saudi Arabia and a more open and more secular Saudi Arabia is good for the region, and good for the world,” he says. “Something we should be all happy about.”