In his announcement, Mr. Hariri said he feared for his life and condemned Iran and Hezbollah in sharp language. The tone contrasted noticeably with the more measured approach he has taken toward Hezbollah and its Lebanese political allies in recent months, even as he has been frustrated with a sense that his side has compromised more than theirs.
The resignation was the first in a series of surprising events that shook the region over several days this month. That same night, Prince Mohammed also presided over the arrests of more than 200 Saudis on corruption charges in what his critics saw as a move to consolidate power. Also that night, Saudi forces claimed to have shot down a missile fired at the capital, Riyadh. Saudi officials blamed Iran-aligned Yemeni rebels for the attack and said the missile amounted to an act of war by Iran and Lebanon.
The startling confluence of events raised fears of increasing escalation in the Saudi-Iranian power struggle, and worries that a new war could break out.
The concerns set off a scramble to de-escalate the situation by international and Lebanese officials and diplomats, who are still struggling to understand the events and what Saudi goals and plans may have been behind them.
Lebanon’s foreign minister, Gebran Bassil, embarked on a tour of Western European capitals to call for Mr. Hariri’s return, and France intervened, with President Emmanuel Macron inviting Mr. Hariri and his family to Paris. On Saturday, Mr. Hariri traveled to Paris with his wife. Their oldest child met them there while their two younger children remained in Riyadh, where they were said to be in school.
From there Mr. Hariri flew on Tuesday to Cairo, where he met President Abdel Fattah el-Sisi of Egypt and discussed “the stability of Lebanon,” he said.
The entire episode, playing out over more than two weeks, turned Lebanese politics upside down. If Mr. Hariri’s resignation is official, the government would face a contentious reshuffle, barely a year after Mr. Aoun and Mr. Hariri took office in a deal that ended years of political stalemate.
Lebanon, a tiny Mediterranean country, is already struggling with the overflow from the war in neighboring Syria, hosting well over a million Syrian refugees amid tensions over Hezbollah’s decisive role in backing President Bashar al-Assad of Syria against a six-year insurgency.
Hezbollah, a bitter rival of Mr. Hariri’s party, was leading the calls for his return. Posters of Mr. Hariri went up around Beirut, the capital, some of them put up by his political opponents.
Lebanese social media satirists delivered a flurry of memes and jokes. One showed a mock movie poster for “Saving Private Saad.” Another depicted Lebanon before and after “Saudi threats.” Both “Before” and “After” were illustrated by the same photograph of an elderly man in a suit jacket smoking a water pipe on a plastic chair on a rock by the sea.
His return coincides with Lebanon’s Independence Day, a holiday that Lebanese observe with a mix of pride, aspiration and irony, given the way the country has been batted about between international powers, from the colonial era to the 15-year civil war a generation ago that ended with both Syrian and Israeli troops, among others, in the country.
Mr. Hariri is likely to be pressed to answer many questions about his plans and his experiences during his mysterious journey.
Some of his closest aides and advisers said that they had little contact with him during his stay in Saudi Arabia, and that they had not known that he was planning to resign. Even after he gave a live television interview insisting he was “free,” many remained unconvinced.
Saudi Arabia maintains considerable leverage over him. His family fortune is entwined with the country, where his father made a fortune in construction, and two of his children remain there.