President Bashar al-Assad’s political survival was under threat on Saturday as the Syrian government battled opposition rebellions around the country and one of his most important allies, Iran, pared back military support.

By Saturday, the main rebel offensive that began on Nov. 27 had reached the outskirts of the strategic city of Homs, only about 100 miles from the seat of Mr. al-Assad’s power in the capital, Damascus. The group leading the offensive said it was preparing to surround the capital.

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

The new uprisings present the most serious challenge in years to Mr. al-Assad. And it is unclear how long he can hold onto the rapidly shrinking pocket of territory under his control, especially without the help of one of his staunchest allies, Iran.

The government in Tehran has lent robust military support that was crucial to Mr. al-Assad’s survival over the past 13 years of 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 Assad 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.”

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

Syrian government forces are stationed on the outskirts of Homs and were shelling areas newly captured by the rebels, according to a British-based war monitoring group, the Syrian Observatory for Human Rights. There were also clashes between rebels and government forces north of the city, the Observatory said.

“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 now approaching Homs 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.

After climate change brought another year of record-breaking heat and dwindling rainfall to Greece, the reservoirs that supply water to Athens have dropped to their lowest levels in over a decade. Farmers are struggling to produce crops, wildfires have increased the demand for water and priests are conducting prayers for rain.

So in addition to investing in modern water-sourcing measures like a new connection to an artificial lake and desalination units, Athens is turning to an older asset: an aqueduct that dates back to when Greece was part of the Roman Empire.

“We have an ancient monument and feat of engineering that we’re bringing into the present to save water and cool the city,” said Katerina Dimitrou of the Athens Water Supply and Sewerage Company, which has worked with the Culture Ministry and local authorities to revive the aqueduct.

The aim is to supplement the water supply, help cool areas by irrigating green spaces and, more broadly, said Ms. Dimitrou, “create a new water culture.”

Known as Hadrian’s Aqueduct, after the Roman emperor who commissioned it in the second century A.D. so that Romans could have baths, the structure then supplied Athens with water for centuries — barring a hiatus during Greece’s Ottoman occupation, when much of it was damaged.

Its 15-mile mostly underground network still runs beneath the city, and the local authorities describe it as Europe’s longest functional underground aqueduct. It also basically still works, carrying water from riverbanks and aquifers along a sloping route.

But after Athens’s first major dam was built in the early 20th century to meet a growing demand for water, the aqueduct was largely abandoned.

“It still works, but the water is wasted,” said Christos Giovanopoulos, a project manager at the local authority of Halandri, an Athens suburb that is a testing ground for the initiative. “It flows all the way to the central reservoir and then joins the sewage system and is expelled into the sea. Nobody uses it.”

Now, a new two-and-a-half-mile pipeline tapping into the aqueduct will provide scores of homes as well as schools and parks with a new water source by March, Mr. Giovanopoulos said. Homes closest to the pipeline will be directly connected, and those farther away will be supplied by trucks, he said, noting that the water will be free for the first six months.

The water, which is non-potable, will be destined for washing and gardening to help conserve drinking water that would otherwise go to such uses. The eventual aim is to extend the project to another seven municipalities under which the aqueduct runs, saving over 250 million gallons of water per year, Mr. Giovanopoulos said.

This is a fraction of the more than 100 billion gallons of water used annually in Athens, those behind the pilot project acknowledge. But the aqueduct route will also irrigate green spaces, which provide a natural cooling effect.

The pilot project, which was supported by 3.1 million euros, about $3.3 million, in European Union funding, has also won international acclaim for urban innovation and is serving as a model for other European cities.

Project organizers are sharing their know-how with other cities, including Serpa, Portugal, which hopes to repurpose a 17th-century aqueduct to irrigate green areas and supply local homes, and Rome, where there is interest in the collaborative nature of the Athens initiative, particularly citizens’ participation.

Miguel Serra, of Serpa’s municipal authority, said the Athens project had “fantastic ideas to promote,” such as “the reuse of water for public irrigation or to create new green areas, and the connection with the local community.”

Many in Athens are unaware of the aqueduct or the rejuvenation plans, including in the surrounding area. Its central reservoir is in a public square called Dexameni — Greek for reservoir — which draws crowds for an open-air cinema and a cafe that was a meeting point for Greek writers in the early 20th century.

“Ninety-five percent of customers don’t know the aqueduct exists,” said Nektarios Nikolopoulos, 48, the cafe’s owner. “They know Dexameni for the cafe, not its history.”

So the local authorities partnered with a nonprofit group to raise awareness about the aqueduct by leading tours of ground-level landmarks like the central reservoir, which visitors can view through windows on its facade.

Yet hundreds of Halandri residents have been instrumental in getting the project off the ground.

Christina Christidou, 56, is one of about 250 residents who have applied to have their homes connected to the aqueduct water. Though initially also unaware of the aqueduct, she has helped organize workshops for the community and schools, which helped revamp green spaces above the aqueduct’s route.

“We used to leave the shower running, but now we’re anxious about how much water we can use,” said Ms. Christidou, a member of Hadrian Community, an association lobbying for residents to manage the distribution of the aqueduct’s water.

Prompting a broader shift in mentality will take time, officials said. But they said the aqueduct offered a forward-looking perspective.

“You can discourage people from using water or encourage them to use other sources,” said Mr. Giovanopoulos, the project manager. “This is more positive.”

President Yoon Suk Yeol of South Korea grew increasingly isolated on Friday, after the head of his ruling party came out in support of impeaching the president, and the country’s military said it would not follow any orders to reimpose martial law.

In a surprise about-face, the leader of the governing People Power Party, or P.P.P., called Mr. Yoon unfit to lead South Korea after his short-lived martial law decree earlier this week catapulted the democracy into turmoil.

“I think that President Yoon Suk Yeol should be suspended from office as soon as possible,” Han Dong-hoon said during an emergency party leadership meeting.

It was not clear how many members of the party shared Mr. Han’s view. But his comments increased the likelihood that the impeachment bill against Mr. Yoon would gain enough support to pass through the National Assembly.

Mr. Han joined opposition lawmakers in warning that if Mr. Yoon stays in office, he might try to impose martial law again in a desperate attempt to hold onto power. In a powerful rebuttal to Mr. Yoon, the defense ministry said that even if he did, the military would not follow. And the country’s special forces command, which joined Mr. Yoon’s ill-fated martial law, said it would not join another.

“I want to make it clear that it will never happen,” Lieutenant General Kwak Jong-geun said during an interview he gave to two opposition lawmakers that was broadcast live on YouTube on Friday, where he was asked about the possibility of another martial law attempt. “Even if I get such an order, I will reject it.”

A broader closed-door meeting of the P.P.P.’s 108 lawmakers took place inside the National Assembly but adjourned without reaching consensus on Mr. Yoon’s fate. Mr. Yoon, though expected at the meeting, didn’t show up. National Assembly Speaker Woo Won-shik said he could not guarantee the president’s safety as angry opposition members rallied at the Assembly’s entrance, chanting “Arrest Yoon Suk Yeol!”

An impeachment vote is scheduled for Saturday evening. At least eight votes from Mr. Yoon’s governing camp are needed to impeach the president.

If impeached, Mr. Yoon would be suspended from office until the Constitutional Court decides whether to reinstate or remove him.

The opposition proposed impeaching Mr. Yoon this week, arguing that he had committed “insurgency” and other anti-constitutional crimes when he declared martial law on Tuesday night. He banned all political activities and sent troops to take over the National Assembly. Legislation on martial law banned such acts, the opposition said in its impeachment bill formally submitted on Thursday.

Mr. Yoon’s surprise declaration of martial law lasted only six hours, until early Wednesday. He was forced to lift it after a vote in the Assembly to repeal the military rule. The short-lived episode, which the opposition likened to a failed “palace coup” by an extremely unpopular leader, triggered outrage across South Korea. Even if briefly, it also exposed the fragility of the hard-won democracy South Koreans have been proud of.

On Thursday, Mr. Han had said he opposed impeaching Mr. Yoon for fear of creating more national confusion. But he said he changed his mind as more details emerged about what happened in the hours after Mr. Yoon declared martial law, especially indications that Mr. Yoon sought to arrest key critics of his government, including Mr. Han himself.

On Friday he said, “There is fear that if President Yoon stays in office, he may repeat extreme actions like martial law.”

“If that happens, South Korea and its people will fall into a bigger crisis,” he said.

Hong Jang-won, a deputy chief of the National Intelligence Service, told lawmakers on Friday that after declaring martial law, Mr. Yoon told him to work with the military’s Defense Counterintelligence Command to “drag them all in,” according to the opposition lawmaker Kim Byung-kee, who attended the closed-door meeting.

According to Mr. Kim, Mr. Hong told lawmakers that Lt. Gen. Yeo In-hyong, the counterintelligence commander, had shared with Mr. Hong a list of people to locate and detain. They included: Mr. Woo, the speaker of the National Assembly; Lee Jae-myung, the leader of the biggest opposition party; and Mr. Han, the head of Mr. Yoon’s own governing party.

Mr. Hong also told the lawmakers that agents from counterintelligence command had planned to take these politicians to their headquarters in Gwacheon south of Seoul.

On Friday, the P.P.P.’s Mr. Han said he also had similar intelligence that the counterintelligence command had planned to detain key politicians in the name of rounding up “anti-state forces.” But when Mr. Han met with Mr. Yoon on Friday to discuss the crisis, the president denied having had such plans, his office said.

In the YouTube interview, Lt. Gen. Kwak, the special forces commander, said his units were not running arrest squads.

He said that Defense Minister Kim Yong-hyun had instructed him to remove lawmakers from the Assembly hall, where the vote on repealing the martial law order was taking place. But he said he ignored the order.

“I knew I could be punished for disobedience,” Lt. Gen. Kwak said. “But I also thought such an order had legal problems and I told my troops not to go in there.”

Mr. Kim resigned after the martial law collapsed. He has since been barred by prosecutors from leaving the country.

On Friday​, the Defense Ministry said it suspended three officers, including Lt. Gen. Kwak and Lt. Gen. Yeo, from their jobs because of their roles in Mr. Yoon’s martial law.

Opposition lawmakers asked the police to investigate Mr. Yoon and others involved in the declaration of martial law on charges of insurgency. If convicted on those charges, the person the court considers the mastermind of the insurgency faces either the death penalty or life imprisonment.

Mr. Yoon has made no public appearances since withdrawing his martial law decree. A survey by Gallup Korea showed Mr. Yoon’s approval ratings plummeted to a record low of 13 percent in the wake of his martial law decision, dragging down his party’s popularity as well.

The impeachment of Mr. Yoon would strengthen the position of the opposition, which has long accused him of incompetence and abuse of power. But it would thrust his already divided party and Mr. Han’s own political future into deeper uncertainty. Political commentators have said the relationship between Mr. Yoon and Mr. Han has irreparably soured in recent months.

Both Mr. Yoon and Mr. Han were star prosecutors before entering politics. Mr. Yoon appointed Mr. Han as his justice minister and helped make him the chairman of the P.P.P. But Mr. Han, once the most trusted ally of Mr. Yoon, has become one of his most bitter enemies since he started bickering with the president over how to handle allegations of corruption involving the first lady, Kim Keon Hee. Recently, they have often ignored each other even when they sat nearby in public events.

Europe’s efforts to contain a resurgence of nationalism and Russian interference entered dangerous new territory on Friday when Romania canceled a high-stakes presidential election, just two days before a runoff vote that an ultranationalist candidate had been well positioned to win.

The dramatic decision to call off Sunday’s election and annul a first round of voting, which was on Nov. 24, was taken by Romania’s constitutional court, which said it had acted “to ensure the correctness and legality of the electoral process.”

Calin Georgescu, an ultranationalist and the front-runner in Sunday’s aborted vote, in a video statement swiftly denounced the court’s ruling as “a legalized coup d’état” that “took democracy and trampled it underfoot.”

Claiming that he had God on his side, Mr. Georgescu, an Orthodox Christian who often talks of his faith, said a win for his camp was assured because “victory belongs to God.” But he stopped short of calling on his supporters to take to the streets in protest, urging them to “be confident, be courageous and remain faithful to our common ideals.”

“They will not be able to stop us,” he added.

The ruling threw Romania, a strategically important NATO member state that borders Ukraine, into political tumult, escalating a crisis that began last month when Mr. Georgescu stunned Romania’s political establishment by winning the opening round of the race for the presidency against 13 other candidates.

It is the worst bout of political turbulence in Romania since the overthrow and summary execution of its communist dictator Nicolae Ceausescu on Christmas Day in 1989, highlighting the perils facing Europe as it wrestles with a surge of nationalist sentiment, particularly in countries on its formerly communist eastern fringe.

The constitutional court ordered a redo of the entire election, including the first round, at a time to be chosen by the government. That could take a while as Romania first needs to form a new government following inconclusive legislative elections last Sunday that left Parliament bitterly divided between centrist and far-right forces.

“Shame!!! A coup d’état is underway,” George Simion, a far-right politician who had endorsed Mr. Georgescu in Sunday’s canceled vote, said after the court decision on Friday. His party, the Alliance for the Union of Romanians, finished second in the election for Parliament.

The court explained its decision to overturn the presidential election result by saying on its website that the race for the presidency had been “flawed throughout its entire duration and at every stage.” It cited manipulation of digital media, apparently a reference to Mr. Georgescu’s use of TikTok videos that were not labeled as campaign material and that mysteriously flooded the mobile phones of Romanians just before the first round vote.

The government has accused TikTok of violating Romanian regulations and has said that Russian-managed bots were in part responsible for spreading Mr. Georgescu’s campaign message, which included calls for peace in Ukraine and an end to European support for Kyiv against Russia’s full-scale invasion.

Information collected by Romania’s security services and released publicly on Wednesday provided no direct evidence of Russian meddling but detailed a highly organized “guerrilla” campaign using social media platforms that resembled well-documented disinformation operations by Moscow in neighboring Moldova ahead of a presidential election there last month.

In a statement on Friday, TikTok said it prohibited “covert influence operations” and had removed three “covert influence networks” in Romania in recent months. The statement followed an announcement by the European Union that it had sent TikTok an urgent request for more information about Romanian intelligence service files indicating that Russia had coordinated posts on the social media platform to promote Mr. Georgescu’s presidential campaign.

Romania’s president has limited powers, but they include overall command of the armed forces, a big say in military spending and oversight of foreign policy. Most of the economic and other domestic policies proposed by Mr. Georgescu would fall outside the usual ambit of the president’s authority.

Mr. Georgescu has voiced admiration for President Vladimir V. Putin of Russia and Romanian fascists of the 1930s and 1940s during World II. He has also repeatedly criticized European military assistance and other help for Ukraine, echoing the views of Hungary’s authoritarian prime minister, Viktor Orban.

Advancing a nationalist economic agenda to combat what he sees as foreign exploitation, Mr. Georgescu has called for the nationalization of certain businesses and a crackdown on foreign corporations.

A skeptic of vaccines and the pharmaceutical industry, he wrote the foreword to the Romanian edition of a book by Robert F. Kennedy Jr., President-elect Donald J. Trump’s pick to be health secretary.

In the now canceled runoff vote, Mr. Georgescu had been set to face off against Elena Lasconi, a centrist mayor and former journalist who had cast the election as a choice between Russia and the West.

Ms. Lasconi also denounced the court’s decision to upend the election. She characterized the ruling as “throwing Romania into anarchy” and “destroying democracy.” The election, she said, should have been held no matter the outcome because “we should have respected the will of the people even if we don’t like it.”

But the nation’s outgoing president, Klaus Iohannis, said that he supported the surprising order. In an address to the nation on Friday evening, he said a redo of the election was “a matter of national security,” citing “information from the services” showing that the campaign of a candidate that he did not name “was supported by a foreign state interfering in Romania’s interests.”

Mr. Iohannis on Wednesday declassified information gathered by security services that suggested Russia had targeted Romania for “aggressive hybrid action” during the election campaign, during which Mr. Georgescu went from a little-known fringe candidate whom many dismissed to a serious contender for the presidency.

His victory shocked Romania’s mainstream parties, the two biggest of which have traded power since the collapse of communism in 1989. It also alarmed Western allies who are worried by a steady rise in Russia-friendly and Ukraine-averse sentiment in Hungary, Slovakia and other parts of East and Central Europe.

Hailing his first-round win as a triumph for the people who “exposed the corrupt, mafia system,” Mr. Georgescu said on Friday said that Romania’s “democracy is under attack” from party leaders “trembling with fear” over losing power on Sunday.

“Basically, on this day, the corrupt system in Romania showed its true face,” he said, “namely, that it made a pact with the devil.”

Laura Stefan, a former Justice Ministry official and legal expert with Expert Forum, a research group in Bucharest, accused the government of acting too slowly to expose and counter Russian meddling, warning, “Now it is too late.”

For Mr. Georgescu’s supporters, she added, the last minute decision by the court only “confirmed that a bad and dark system is working against them.”

Alan Yuhas and Steven Lee Myers contributed reporting.