South Korean lawmakers’ attempt to impeach President Yoon Suk Yeol ended in failure on Saturday night, prolonging the political upheaval and uncertainty that has roiled the country since his short-lived imposition of martial law this week.

The failed vote was a reversion to political deadlock in the deeply divided country, despite large-scale protests calling for the president’s removal. It was a contrast to the brief moment early Wednesday when lawmakers across the political spectrum came together to vote swiftly and unanimously against the president’s martial law declaration.

Saturday’s move by the opposition to impeach Mr. Yoon was foiled by his conservative People Power Party, which boycotted the vote and prevented the necessary quorum. All but one member of the party walked out of the room before the impeachment motion was put to a vote, making the effort moot even before the first ballot was cast.

The opposition drew out the vote over several hours into the night, urging lawmakers to return to the chamber to participate in the democratic process, in the very building that had been stormed days earlier by hundreds of soldiers acting under martial law orders.

“The South Korean people were watching our decision today. Nations around the world were watching us. It is utterly unfortunate that the vote effectively didn’t occur,” the assembly speaker, Woo Won-shik, said as he called the session to a close.

Earlier on Saturday, Mr. Yoon bowed before the nation and apologized in a brief televised address, his first public appearance since the move to install martial law. He said that he had taken the step out of desperation, and that he would not try to avoid legal or political responsibility for the martial decree.

But Mr. Yoon — who keeps on his desk a plaque given to him by President Biden with the words “The buck stops here” — made no mention of resigning, or of the impending impeachment vote.

As the week wore on, Mr. Yoon had appeared increasingly isolated, with members of his party openly criticizing the decision and casting doubt on his political future. The apology appeared to be a last-ditch attempt to avoid impeachment in the National Assembly by putting his fate in his party’s hands.

Ultimately, partisan politics appeared to prevail. The leader of Mr. Yoon’s party, Han Dong-hoon, said before the vote that the president could not carry out his duties and should not serve out his term. Even so, he did not specifically mention impeachment, leaving open the possibility of an alternative resolution.

Despite surviving the impeachment attempt, it is unlikely Mr. Yoon will be able to carry out any significant government business or represent the country after his failed decree, which was nearly universally condemned.

Lawmakers from the opposition Democratic Party, invigorated by the widespread anger toward Mr. Yoon, said they would continue their efforts to impeach the president in future sessions. But there were questions, too, about whether their party had scuttled its own effort by moving before it had secured enough political support.

Now, South Korea faces a protracted battle over its leadership at a time of deep geopolitical insecurity. North Korea, with its growing nuclear weapons capability, has greatly intensified its threats against the South. And the change of administrations in the United States, its most important military ally, could complicate cooperation between the countries.

Though his party’s walkout seemed to buy Mr. Yoon some time, another threat is looming: South Korean prosecutors said Saturday that they had launched a criminal investigation into the declaration of martial law on Tuesday night.

As the assembly weighed Mr. Yoon’s fate Saturday afternoon, huge crowds of protesters filled the eight-lane-wide street outside, demanding his ouster late into the night despite below-freezing temperatures. Buses and vans were left parked across open spaces around the assembly, out of concern that troops might once again attempt to land there by helicopter, as they did earlier this week when they stormed the legislature.

The images of armed soldiers moving against lawmakers and demonstrators raised painful memories of the traumatic period of the country’s recent history when the military indiscriminately killed civilians and quashed political opposition with force.

The upheaval has brought a wider swath of the South Korean public onto the streets, with younger demonstrators joining with some of the generation who defied the military and helped usher in the country’s democracy four decades ago.

But in a sign of the continuing divisions cleaving the country, a smaller group gathered across town in support of the president. The people in that crowd barely mentioned the martial law declaration that started the crisis. Instead, many focused on branding the opposition as Communist sympathizers who endangered the country, echoing one of Mr. Yoon’s favored lines of attack.

Many of the protesters calling for Mr. Yoon’s removal said they felt compelled by the president’s actions to take to the streets despite never having been to a political gathering before.

“There’s been a wakeup call to become more aware,” said An Ye-young, 19, who said this was her first protest. “It’s meaningful that people can express their will in a united way like this.”

And like the opposition lawmakers, protesters said they would not let up in voicing their displeasure with the president.

“I plan to come every weekend,” said Subin Park, 29.

Reporting was contributed by Choe Sang-Hun, John Yoon and Brolley Genster.

President Volodymyr Zelensky of Ukraine met with President-elect Donald J. Trump in Paris on Saturday, the first face-to-face encounter between the two since Mr. Trump won the U.S. presidential election last month after claiming that he would end the war in 24 hours.

Mr. Trump and Mr. Zelensky were brought together by President Emmanuel Macron of France at the Élysée Palace on Saturday evening, ahead of the Notre-Dame Cathedral’s grand reopening. It was a diplomatic coup for the French leader, who is otherwise facing a political crisis at home after his government fell this week.

While it was not immediately clear what was said in the meeting, Mr. Zelensky was expected to press Ukraine’s case to Mr. Trump, amid concerns that his pledge to end the war quickly could leave Kyiv sacrificing substantial territory to Russia and lacking the security guarantees needed to deter future aggression.

Mr. Zelensky said afterward that it had been a “productive meeting” and he thanked Mr. Trump for his determination and Mr. Macron for organizing the encounter.

“We talked about our people, the situation on the battlefield and a just peace for Ukraine. We all want to end this war as quickly and fairly as possible,” the Ukrainian leader said in a statement, adding that they had “agreed to continue working together.”

The meeting appeared to be part of a broader diplomatic push by Ukraine to engage with Mr. Trump’s incoming administration and influence its plans to end to the war with Russia in a way that aligns as much as possible with Kyiv’s interests. Earlier this week, a delegation of senior Ukrainian officials traveled to the United States to meet with several of Mr. Trump’s key appointees.

“What is happening now is just the first act of a prelude to the negotiations to come,” Volodymyr Fesenko, a Ukrainian political analyst, wrote in a post on Facebook about the Ukrainian delegation’s visit to the United States.

Both Mr. Trump and Mr. Zelensky were slated to attend the reopening of Notre-Dame Cathedral in Paris, but it remained uncertain until the last moment whether they would meet. They eventually spoke at the Élysée Palace, in what appeared to be a carefully choreographed entrance.

Mr. Macron greeted Mr. Trump at the Élysée Palace at 4:45 p.m. local time. Around 45 minutes later, Mr. Zelensky’s car pulled into the palace courtyard. The Ukrainian president stepped out, ascended the red-carpeted stairs, and entered the 18th-century building to join the French and American leaders.

They posed for pictures ahead of the trilateral meeting, which lasted about 30 minutes. “United States, Ukraine, and France. Together on this historic day. Gathered for Notre-Dame. Let us continue our joint efforts for peace and security,” Mr. Macron wrote in a social media post which included a picture of them talking under the gilded halls of the Élysée Palace.

Then the three leaders shook hands at they exited the palace, heading to the reopening ceremony of Notre-Dame Cathedral.

The event had been seen by Ukraine as a chance to press its case to the dozens of world leaders in attendance. Mr. Zelensky said he had met with Karl Nehammer, the Chancellor of Austria, and Salome Zourabichvili, the president of Georgia.

Sounding out Mr. Trump on his plans to end the war has been a top priority for Ukraine. These plans have so far been unclear, but officials in Kyiv are concerned that Mr. Trump’s vague pledge to end the war in 24 hours could result in Russia keeping the territory it has captured and ignoring Ukraine’s demand to join NATO as a security guarantee to prevent further attacks.

Ukraine’s outreach to Mr. Trump’s team has coincided with an apparent shift in Kyiv’s public stance on peace talks. After years of vowing not to cede territory to Russia, Mr. Zelensky has recently suggested he would consider doing so as a way to end the war, in return for NATO membership. Ukraine, he added, would then seek to regain its occupied territory through negotiations.

The change in position has been seen as a way for Ukraine to show Mr. Trump that it is ready to make concessions as part of negotiations. By contrast, Ukraine officials have insisted that Russia didn’t want to engage in negotiations, especially as its troops are steadily gaining ground on the battlefield.

Before Saturday’s meeting, Mr. Zelensky had already spoken with Mr. Trump three times this year: in a phone call over the summer, during a meeting in New York in September and in another call shortly after Mr. Trump’s election last month.

In an interview with Sky News last week, Mr. Zelensky said he wanted to work with Mr. Trump “directly” and was open to his proposals. “I want to share with him ideas, and I want to hear from his ideas,” he said.

President Bashar al-Assad’s political survival was under threat on Saturday as the Syrian government battled opposition rebellions around the country and the strategic city of Homs was breached by the main rebel coalition, according to the fighters and a war monitor.

The rebels then declared early Sunday that they had fully captured the city, not long after the Syrian defense ministry denied that rebels had entered Homs, which is only about 100 miles from the seat of Mr. al-Assad’s power in the capital, Damascus. The ministry said in a statement that the situation remained “stable and secure.”

Anti-government protests took place near Damascus on Saturday, and Mr. al-Assad’s forces withdrew from several of its suburbs, according to war monitoring groups.

The Syrian military denied that its forces had withdrawn from the suburbs. Yet Mr. al-Assad’s autocratic government, which had until just over a week ago appeared to have a firm grip over much of the country, now seemed to be facing a possible breach of the capital.

The new uprisings present the gravest challenge in years to Mr. al-Assad. It is unclear what resources he can marshal to defend the rapidly shrinking territory under his control, especially without the help of one of his staunchest allies, Iran, which began to evacuate its military commanders and personnel from Syria on Friday.

Russia, his other important ally through nearly 14 years of civil war, has offered only limited aid.

The British-based war monitor Syrian Observatory for Human Rights said government forces have pulled out of a number of suburbs of the capital, including Moadamia al-Sham and Daraya, and the nearby Mezzeh military airport. That could not immediately be confirmed.

The Observatory also reported that residents of another Damascus suburb, Jaramana, came out in an antigovernment protest, chanting anti-Assad slogans and pulling down a statue of Hafez al-Assad, the current president’s father and predecessor.

Syrian state media reported that Mr. al-Assad was still in Damascus.

Mr. al-Assad’s control in southern and northeastern Syria, too, appeared to be crumbling, with a different coalition of rebel factions capturing much of Daraa Province in the south, and U.S.-backed Kurdish-led forces moving into the city of Deir al-Zour in the northeast, according to the Observatory.

The group leading the main offensive said it was preparing to surround the capital, which rebels had attacked early on in the civil war but had not entered since.

“Our forces have begun implementing the final phase of encircling the capital Damascus,” a rebel commander, Lt. Col. Hassan Abdulghani, said on Saturday afternoon in a statement posted on the rebels’ Telegram channel. He gave no further details and it was not immediately clear whether any operation on the ground near Damascus was underway.

“We have started sending more reinforcements from the north and south to the axes of the capital Damascus to support our ongoing operations there,” he said hours later.

Russia and Iran both lent robust military support to Mr. al-Assad over the last decade, proving crucial to his survival through Syria’s civil war.

But late on Friday, Iran moved to start evacuating military commanders and other personnel from Syria, according to Iranian and regional officials.

There were also few signs that another major ally, Russia, was coming to the Syrian government’s aid, beyond some limited airstrikes. Russia intervened in Syria’s civil war in 2015 and helped keep Mr. al-Assad in power by bombarding rebel-held areas into submission. But now the Russian military is stretched thin, with much of its air and ground force tied up in Ukraine.

Analysts said Russia sees little incentive to intervene more forcefully in Syria given the apparent ineffectiveness of Mr. al-Assad’s own forces.

“The Syrians need to be the ones defending Homs,” said Anton Mardasov, a Moscow-based military analyst focusing on the Middle East. “If they are running away, then no one will be fighting in their place.”

Earlier Saturday, the opposition fighters in Homs faced some of the stiffest resistance they have encountered so far from the government forces there, who are trying to block the rapidly moving rebel advance heading toward Damascus.

Syrian government forces were stationed on the outskirts of Homs and were shelling areas newly captured by the rebels, according to the Observatory. There were also clashes between rebels and government forces north of the city, the war monitor said.

But by early Sunday morning, the rebels and the Observatory said fighters had breached the city.

“Syria is witnessing a historic change,” the rebels said in a statement released on their official Telegram channel. “And the people’s message has become clear: There is no place for injustice, no return to tyranny, and the end is closer than Bashar imagines.”

An array of different groups have been taking territory from the government in other parts of the country as well.

Government forces and their Russian allies withdrew from more than a dozen positions in the southwestern province of Quneitra near Israel and rebels took over the positions, according to the Observatory.

In eastern Syria, government forces in the city of Deir al-Zour have nearly entirely withdrawn from their positions, including from the airport and a military base, according to the Observatory. In their place, Kurdish-led forces backed by the United States have sent military reinforcements and released prisoners from a military prison there, the war monitoring group said.

With Syria’s allies pulling back, the weakness of the national military has come on full display.

Despite four years of a frozen conflict, analysts say the Assad government has done little to strengthen its military ranks, confident in an ultimate victory over the opposition. Instead, the military ranks remain filled with unwilling and poorly paid conscripts, young men forced into military service.

On Wednesday, Mr. al-Assad ordered salaries for his forces increased by 50 percent. But that was not expected to prevent more soldiers from fleeing the front lines.

U.S. officials, speaking on condition of anonymity, said Damascus could soon be under threat. A senior State Department official said Mr. al-Assad needed ground forces and that Iran would be hesitant to provide any.

The U.S. Embassy in Damascus on Friday urged U.S. citizens to leave Syria now.

“The security situation in Syria continues to be volatile and unpredictable with active clashes between armed groups throughout the country,” an Embassy statement said.

The main rebel offensive charging south toward the capital is led by the Islamist group Hayat Tahrir al-Sham. It has taken major cities and large parts of four provinces since launching a surprise offensive last week out of its base in northwestern Syria.

In the southern province of Daraa — where the Syrian uprising against Mr. al-Assad’s authoritarian rule began in 2011 — a separate grouping of local rebel factions has taken control of more than 80 percent of the province after government forces withdrew from checkpoints and military headquarters, according to the Observatory.

And in the neighboring province of Sweida, a different array of local opposition groups attacked police and military checkpoints and took control of the main prison.

Anton Troianovski contributed reporting.

As armed rebels have advanced at lightning speed in recent days from the north of Syria toward the capital, Damascus, footage online showed statues of the Assad dynasty — which has kept the country in its authoritarian grip for over 50 years — crashing to the ground.

But as the figures of President Bashar al-Assad’s deceased father and brother fell to cries of “God is Great!” the question looming over the astonishingly rapid resurrection of the torpid civil war into a five-alarm fire is whether the rebels might topple the president himself.

The commander of the rebel alliance, Abu Mohammed al-Jolani, who depicts himself as a reformed zealot from Al Qaeda, has bluntly made that point.

“Our goal is to liberate Syria from this oppressive regime,” he said in a video interview with The New York Times.

Whether the rebels succeed or not, experts believe that an expected brutal fight to control Damascus, and by extension Syria, would constitute the most important confrontation yet in the struggle to remake the region, one ignited on Oct. 7, 2023, with the Hamas-led attack on Israel.

The main regional players — Israel, Iran and Turkey — all have a stake in the outcome, which means that the ripples will affect not just the Middle East, but also global powers like the United States and Russia.

If the war in Gaza is the worst manifestation yet of the seemingly intractable Israel-Palestinian dispute, which drew in the armed Lebanese group Hezbollah, analysts call the fight for Syria a far more important struggle to dominate a regional crossroads that influences the entire Middle East.

“Syria is the barometer for how power dynamics in the region are changing,” said Mona Yacoubian, head of the Middle East and North Africa Center at the United States Institute of Peace in Washington. “It is in for a period of chaos in a region that is already on fire.”

Israel’s strategists refer to Syria as the “hub of hubs,” which has served as a supply conduit for men and arms to places like southern Lebanon. There, Hezbollah, Iran’s main regional ally, held sway before Israel decimated the group’s ranks by assassinating its longtime leader and much of his top echelon. Israel also launched direct attacks on strategic air defenses in Iran.

Israel is determined to prevent Iran, which has propped up the Assad regime, from re-establishing those supply lines. It is also not clear how Israel would react to an Islamic-style government in Syria should Mr. al-Assad’s regime fall, especially a government beholden to Turkey’s president, Recep Tayyip Erdogan, who has been a harsh critic because of the Gaza war.

Iran knows that if it loses Mr. al-Assad and its sway over Damascus, it is game over for its attempt to fortify a crescent of Shiite Muslim proxy forces from Lebanon to Iraq to Yemen that can threaten Israel. Nonetheless on Friday, Iran, after more than a decade of staunch support for Mr. al-Assad, began evacuating top military commanders of its powerful Quds Forces and other personnel from Syria, according to Iranian and regional officials.

Some analysts see the hand of Mr. Erdogan in the sweeping advance of the main Syrian rebel group, Hayat Tahrir al-Sham, or the Organization for the Liberation of the Levant. Turkey seized an opportunity to increase its influence at a time when Iran was beleaguered, analysts said, and it wants the three million Syrian refugees who fled to its territory because of the civil war to return home.

Damascus is the target, Mr. Erdogan told reporters after Friday prayers in Istanbul. “The opposition’s march continues,” he said. “Our wish is that this march in Syria continues without incident.”

In Russia, which had made bolstering Mr. al-Assad a cornerstone of its Middle East policy for almost a decade, President Vladimir V. Putin faces a dilemma: beef up his country’s forces there to aid Syria and risk shortchanging his troops in Ukraine, where he needs every hand to prosecute the war.

In a telling sign of diminishing confidence, Russia announced on Friday that its citizens should leave Syria.

Russia and Iran are not the only nations ordering evacuations.

The U.S. State Department also encouraged Americans to leave. Washington has not known quite what to do about Syria for more than a decade, basically letting its policy drift after Russia moved in 2015 to intervene there militarily, analysts said. Now, Washington faces a moment of transition between two administrations, with the incoming president, Donald J. Trump, having once referred to Syria as “sand and death.”

It is unclear how much time all these governments have to act, given the volatile situation on the ground. In little over a week, the Syrian rebels have captured two of the country’s most important cities along the north-south corridor that forms the country’s main spine.

The rebels have been preparing for this offensive for more than a year, said Ibrahim Hamidi, the Syrian editor of Al-Majalla, an online current affairs magazine based in London. On the surface, the war might resemble the period around 2014, when Mr. al-Assad was on the ropes, and Iran and Russia intervened. That was then.

“The whole equation is different now,” said Mr. Hamidi.

Iran and Hezbollah, the main forces buttressing the regime, have been seriously weakened from their fight with Israel. And Russia, whose air force used to carpet-bomb Syrian rebel strongholds, is preoccupied by its war in Ukraine. While Russia has resumed aerial bombardments in Syria, it is on a far smaller scale.

First to fall was the city of Aleppo, the economic capital, and then Hama, the breadbasket. The rebel forces are now putting pressure on Homs, which is a little over 100 miles north of Damascus and the strategic hinge linking the country’s heartland to the Mediterranean Sea and the coastal center of the Alawites, a minority Shiite Muslim sect that dominates the regime.

Civilians began to flee Homs in earnest on Friday.

Syria has relied heavily on Iranian militias for ground troops. But Israeli missile attacks on Syria have thinned the ranks of senior Iranian militia commanders, as well as supply lines.

And on Friday, Kurdish forces in northeast Syria, who have long been buttressed by a contingent of about 900 U.S. troops, reportedly took control of the main border crossing that Iranian forces used to enter Syria from Iraq.

As for Hezbollah, in 2013, its forces poured over the border from Lebanon to smash the armed opposition at Qusayr. And some of its men have now deployed to defend Homs, said a Hezbollah official in Damascus, speaking on condition of anonymity for security reasons.

But after months of fighting Israel in Lebanon, it is unclear how many forces Hezbollah has left to deploy to Syria.

When it comes to the Syrian Army, some of the strongest units, the Fourth Armored Division and the Republican Guards, have long been stationed around Damascus with the idea of making it coup-proof. But lack of training and low salaries have taken their toll, with regular troops melting away rather than confronting the rebels.

“You need loyal, reliable troops to hold territory, and they are not there,” said Andrew J. Tabler, a senior fellow at the Washington Institute for Near East Policy and a former U.S. government official on security issues.

Many analysts consider the central Syrian state a hollow shell. “The Assad regime is unbelievably rickety,” Mr. Tabler said. “It is like an old car put together with spare parts by unknown mechanics.”

Since the Obama administration, Washington has been fearful of what was called “catastrophic success”: having Mr. al-Assad fall, only to be replaced by a jihadist regime. That fear remains, although Mr. Jolani, who has held authoritarian control of northwestern Idlib Province for years, attempted through outreach to minorities and other moderate steps to recalibrate his reputation as a religious nationalist rather than a jihadist.

The alliance, which broke ties with Al Qaeda in 2016 but remains labeled a terrorist organization by the United States, the European Union and the United Nations, has become a broader coalition that includes more moderate factions.

Yet, memories of the disasters that accompanied the effort to glue together a coalition Iraqi government are still fresh.

“This is all about the balance of power between these regional players in the Levant, where Syria sits at the heart,” said Firas Maksad, a senior fellow and Syria expert at the Middle East Institute based in Washington.

Raja Abdulrahim, Hwaida Saad and Farnaz Fassihi contributed reporting.

For decades, Iran has expended much blood and money in support of Syria’s president, Bashar al-Assad, helping him survive a civil war that threatened his dynastic rule. Iran operated military bases, weapons warehouses and missile factories in Syria, which it used as a pipeline for arming its militant allies across the region.

Now, just as Mr. al-Assad needs help to repel a rapid advance by rebel forces, Iran is heading for the exits. On Friday, the country started evacuating its military commanders and personnel, as well as some diplomatic staff, according to Iranian and regional officials.

It is a remarkable turnabout: Iran not only appears to be abandoning Mr. al-Assad, its closest Arab ally, but also relinquishing everything it had built and fought to preserve for 40 years in Syria, its main foothold in the Arab world.

With the rebels expected to advance soon on Damascus, Iran is unable to muster a defense of the Assad government after a damaging year of regional wars that began with the Oct. 7 attack on Israel by Hamas, an Iranian ally.

A collapse of Iran’s partnership with Syria would by all accounts reshape the balance of power in the Middle East. The “axis of resistance” that Iran has formed with its militant allies in Lebanon, the Palestinian territories, Syria, Iraq and Yemen would be weakened. Israel and its Arab allies would be strengthened.

“For Iran, Syria has been the backbone of our regional presence,” Hassan Shemshadi, an expert on Iran’s proxy militant groups who was for years a documentary filmmaker on the battlefields of Syria, said in an interview from Tehran. “Everything that Iran sent to the region went through Syria. It is now extremely difficult to keep these channels open.”

Initially, the Iranian government was shocked at how quickly the rebels in Syria gained ground and the Syrian Army abandoned its bases, according to three Iranian officials, two of them members of the elite Revolutionary Guards, and two prominent Iranian analysts close to the government.

By midweek, the mood had turned into full panic, the officials said, as the rebels were on a march that would hand them city after city, from Aleppo to Hama to Deir al-Zour and Daraa.

Publicly, Iranian officials vowed to remain fully committed to supporting Mr. al-Assad. But privately, as the rebels gained control over more and more territory where Iran and its proxy militias had reigned, they wondered if events were outpacing their ability to turn the tide, the officials said.

By the end of the week, several senior officials had made statements on social media that Mr. al-Assad’s ouster was seemingly inevitable and Iran’s setback monumental.

“The potential fall of the Syrian government to Islamist extremists would be one of the most significant events in the history of the Middle East,” Mohammad Ali Abtahi, a former vice president, wrote on X. “Resistance in the region would be left without support. Israel would become the dominant force.”

Although Iran’s foreign minister, Abbas Araghchi, who has traveled to Damascus, Baghdad and Doha, Qatar, for consultations on Syria, at first struck a defiant tone, he later said that Mr. al-Assad’s fate would be left to “God’s will.”

An internal memo from a Revolutionary Guards member that was viewed by The New York Times described the situation in Syria as “unbelievable and strange.” It is as if “Iran accepted the fall of Assad and has lost the will to resist,” the memo says.

State television in Shiite-majority Iran switched from calling the Sunni rebels “infidel terrorists” to “armed groups” and reported that they had so far treated Shiite minorities well.

Soheil Karimi, a former fighter in Syria turned political pundit, said on a state television news program that Mr. Araghchi’s pledges of support to Syria’s government were nothing but false hope.

“The reality in the field is not what he says,” Mr. Karimi said, citing reports from his contacts in Syria. “Our guys are not in the battlefield in Syria now. They have not been allowed.”

A video posted on Friday on social media accounts affiliated with the Revolutionary Guards showed a Shiite shrine near Damascus almost empty. A narrator says, “These may be the last images you see of the shrine, everyone has left Syria, all the Iranians have evacuated.” He then breaks into sobs.

The shrine, Sayyidah Zaynab, is the tomb of the granddaughter of the Prophet Muhammad, and it has played a central role in Iran’s war narrative in Syria. Iranian soldiers who fought in Syria are commonly referred to as “defenders of the shrine.”

The three Iranian officials said that Hayat Tahrir al-Sham, the main rebel group advancing in Syria, sent Iran a private diplomatic message this week. The group promised that it would protect Shiite religious sites and Shiite minorities and asked Iran not to fight its forces, according to the officials. Iran, in turn, asked the group to allow safe passage of its troops out of Syria and to protect the Shia shrines, according to two officials.

Iran deployed commanders and troops to Syria in 2012 at the start of the anti-government uprising, helping to defeat both the opponents of the Assad regime and the Islamic State terrorist group.

It used its continued foothold in Syria to maintain a robust weapons supply chain to Hezbollah in Lebanon and to Palestinians in the West Bank, including through two shipping ports and airports. More recently, Iran partnered with smuggler gangs and some members of Bedouin tribes in Jordan to send arms from Syria to the West Bank.

But the dynamics of the Middle East have changed vastly in the past year.

Iran suffered significant blows as Israel attacked Iranian assets and bases in Syria, including its embassy compound in Damascus. Israel killed at least two dozen Iranian forces, some of them senior commanders in charge of regional operations, according to Iranian media.

In addition, Iran’s key ally Hezbollah was battered after an intense period of fighting with Israel in Lebanon. Russia, another ally of Syria, is focused on its own war with Ukraine. And more crucially, Syria’s Army has demonstrated an unwillingness to fight.

Yet another concern for Iran was Israel’s threat to attack any mobilization of Iranian troops in Syria, according to analysts inside and outside the country. Two flights by a private Iranian airline en route to Damascus were turned around this past week after warnings by Israel that it would shoot them down if they entered Syria’s airspace, according to Iranian and Israeli officials. Israel said the flights were transferring weapons.

“For Iran to enter this fight it would require massive logistical and financial resources,” as well as help from allies and Syria itself, said Mehdi Rahmati, a Syria analyst in Tehran who has advised the government. “None of these conditions exist right now.”

“Syria and Lebanon are like our left and right wings,” Mr. Hemati said. “They are being clipped, and it’s hard to imagine one without the other.”

Afshon Ostovar, an associate professor of national security affairs at the Naval Postgraduate School in California and an expert on Iran’s military, said Iran was in a bind, particularly with Donald J. Trump returning to the presidency and expected to enforce a policy of “maximum pressure on Iran.”

“Losing ground in Syria will make Iran look increasingly weak to its enemies in Tel Aviv and Washington,” Mr. Ostovar said. “If Iran doubles down on Syria, it could be throwing men and materiel into a losing battle. But if Iran falls back, it will appear weak, be admitting defeat, and cede hard-fought territory to its enemies.”