Lebanon was thrown into turmoil after the sudden resignation of Prime Minister Saad Hariri from Saudi Arabia. Here's what you need to know. (Joyce Lee/The Washington Post)

When Saad Hariri’s jet touched down in Beirut early Thursday, Lebanon hoped it would bring an end to a crisis spurred by his abrupt and mysterious resignation as prime minister, delivered in a speech from Saudi Arabia last week.

But he was not aboard, according to local media and an airport employee.

For five days, Hariri has been in the shadows, his whereabouts and status the subject of fevered speculation in this fragile state. Aides said they have hardly spoken to him. His own political party has anxiously demanded his return.

A growing conviction that Saudi Arabia is restricting his movements has shaken Lebanon, fueling fears that the country, yet again, was becoming a battleground for destructive regional rivalries.

When Hariri resigned on Saturday, during what appeared to be a routine trip to Riyadh, the Saudi capital, he blamed Iran, saying it had created a “state within a state” in Lebanon, a reference to the Iran-backed Hezbollah movement that is the country’s dominant political force. But the resignation — a dramatic gesture that seemed to come out of nowhere — blindsided Lebanon, including Hariri’s supporters.

It was perhaps better explained by the tensions between Saudi Arabia and Iran, a feud that has simmered for decades and, in the past few days, left the region fearing the outbreak of new wars.

Saudi Arabia and its Persian Gulf allies fumed in recent years as Iran reached a deal over its nuclear program with Western countries and expanded its influence in the region, including in Syria and Iraq.

The 32-year-old crown prince of Saudi Arabia, Mohammed bin Salman, has helped lead an aggressive gulf effort to counter the Iranians — most visibly, by mustering a military coalition to fight in Yemen against a rebel group that the Saudis regard as an Iranian proxy force. And President Trump has emerged as one of Saudi Arabia’s closest allies, repeatedly praising the kingdom and its anti-Iranian stance.

In Lebanon, there was immediate suspicion that Hariri — whose speech echoed Saudi Arabia’s own combative rhetoric — had in fact been forced to step down by the Saudis, and become a pawn, along with his country, in the Saudi-Iranian feud.

“Global struggles and antagonisms are often reflected in small countries, and Lebanon is one of them,” said Imad Salamey, a professor at the Lebanese American University. “It is a complicated place because there are multiple confessional groups aligned with regional powers and trying to coexist. We are seeing that reflected back onto the country now, with more confrontation than peace.”

On Tuesday, a few days after his speech, Hariri was seen in the United Arab Emirates, a close ally of Saudi Arabia. Hariri, who has also long been backed by the Saudis, met an Emirati leader, Mohammed bin Zayed, who wished him “all the success in his endeavors to ensure Lebanon overcomes its ordeals and achieves the aspirations of the Lebanese people,” according to the Emirates News Agency.

It seemed a strange thing to say to a politician who had just resigned.

By Wednesday, Hariri was back in Riyadh, according to a statement from his office, which said he met with diplomats from the United States, Britain and the European Union. On Thursday, the statement said, Hariri received the French ambassador.

There was speculation that Hariri was among scores of people detained by the Saudi authorities in the last week, including princes, officials and some of the most prominent businessmen in the country. While Saudi officials insist the arrests — of more than 200 people so far — are part of an aggressive anti-corruption campaign, the sweep is also widely seen as an effort by the crown prince to eliminate rivals and consolidate power.

Many analysts agreed it amounted to a radical restructuring of Saudi Arabia’s political order, a spectacle that riveted the Middle East.

But back in Lebanon, the anxiety only grew.

“We are still in the phase of the unknown,” a senior Lebanese official said Thursday. “We have been meeting with foreign ambassadors and no one has any relevant information. No one was able to talk to Hariri beyond: ‘Hi, how are you? I’m fine.’ ”

The Saudis had forced the prime minister to resign, said the official, speaking on the condition of anonymity to discuss a sensitive political crisis. “It’s not voluntary.” The Reuters news agency, citing two anonymous U.S. officials, said the Saudis had “encouraged” Hariri to leave office.

In a statement on Thursday, Hariri’s Future Movement political party said his return was a “necessity.”

Saudi Arabia ordered its citizens to leave Lebanon “as soon as possible,” citing the “situation” there, according to the Saudi Press Agency. Other gulf states allied with the Saudis, including Bahrain and the United Arab Emirates, did the same.

“If anyone tells you he knows what is going on, then he’s lying,” said Misbah Adnan Eid, an official in the Beirut district of Basta. “There is a sense of loss, a sense of the unknown. We don’t know when this ends.”

Fahim reported from Istanbul.