On a recent morning in eastern Ukraine, Karina Yatsina, a mine worker, was busy operating a conveyor belt in a dim, 1,200-foot-deep tunnel. Lights flickered at the end of the shaft, illuminating miners carving out the coal seams.

A year and a half ago, Ms. Yatsina, 21, was working as a nanny. Then friends told her that a mine in the eastern town of Pavlohrad was hiring women to replace men drafted into the military. The pay was good and the pension generous. It wasn’t long before Ms. Yatsina was walking through the mine’s maze of tunnels, a headlamp strapped to her red helmet.

“I would have never thought that I would be working in a mine,” Ms. Yatsina said, taking a short break in the sweltering heat of the tunnel. “I would have never imagined that.”

Ms. Yatsina is one of 130 women who have started working underground at the mine since Russia’s full-scale invasion of Ukraine began in February 2022. They now operate conveyors that carry coal to the surface, work as safety inspectors or drive the trains that connect the different parts of the mine.

“Their help is enormous because many men went to fight and are no longer available,” said Serhiy Faraonov, the deputy head of the mine, which is run by DTEK, Ukraine’s largest private energy company. Some 1,000 male workers at the mine have been drafted, he said, or about a fifth of the total work force. To help make up for the shortage, the mine has hired some 330 women.

They are part of a wider trend in Ukraine, where women are increasingly stepping into jobs long dominated by men as the widespread mobilization of soldiers depletes the male-dominated work force. They have become truck or bus drivers, welders in steel factories and warehouse workers. Thousands have also voluntarily joined the army.

In doing so, these women are reshaping Ukraine’s traditionally male-dominated work force, which experts say has long been marked by biases inherited from the Soviet Union. “There was this perception of women as second-class and less reliable workers,” said Hlib Vyshlinsky, the executive director of the Kyiv-based Center for Economic Strategy.

Mr. Vyshlinsky said that Ukrainian women had long been excluded from certain jobs, not only over the physical demands but also because such roles were considered too complicated for them. Women, he said, could drive trolley buses, but not trains. “It was full of stereotypes.”

The current influx of women into the Ukrainian job market has echoes of the munitionettes, the British women who worked in arms factories during World War I, and the women — memorialized in the iconic posters of Rosie the Riveter — who went to work in the United States during World War II.

But even with the influx of women into the work force, they will not be enough to replace all the male workers who have left, economists say. Three-quarters of Ukrainian employers have experienced labor shortages, a recent survey showed.

Before the war, 47 percent of Ukrainian women worked, according to the World Bank. Since then, some 1.5 million female workers, about 13 percent of the total, have left Ukraine, Mr. Vyshlinsky said.

“The share of women currently working in Ukraine is higher than before the war,” Mr. Vyshlinsky said. But too many have left Ukraine to allow the country to overcome its work force shortages, he said.

The phenomenon of women joining the work force has been particularly evident in the mining industry.

After Russia invaded in 2022, the Ukrainian government suspended a law that had barred women from working underground and in “harmful or dangerous” conditions. Now, they are a regular presence in the cramped lift shafts that take workers to the depths of the mines.

“I was surprised. It’s unusual to see a woman with a shovel doing a man’s work,” said Dmytro Tobalov, a 28-year-old miner, not long after a woman walked past him and other burly miners who were resting on benches in a tunnel, waiting to board the elevator back out of the mine.

Mr. Tobalov, who works at a mine in Pokrovsk, in the eastern Donetsk region, said 12 men had left his group of miners for the army, replaced by 10 men and two women. “They’re doing great,” he said of the women.

Several women said they had joined the Pokrovsk mine, owned by Metinvest, Ukraine’s largest steel maker, because it offered stable jobs in a war-ravaged economy. Valentyna Korotaeva, 30, a former shop assistant in Pokrovsk, said she lost her job after a Russian missile landed near the shop, causing the owners to pack up and leave. She now works as a crane operator at the mine, moving large metal machines under repair in a warehouse.

How long Ms. Korotaeva can keep her job will depend on the situation on the front line, just eight miles from the mine. Russian forces have been creeping closer to Pokrovsk in recent weeks. Russia frequently shells the area, and the mine’s management has prepared evacuation plans in case it becomes too dangerous to remain there.

“It’s scary,” Ms. Korotaeva, a mother of two, said. “But for now I’m staying because there are schools and kindergartens here. There’s nowhere else to go.”

Several women said working in a mine was a way to participate in the war effort, keeping the Ukrainian economy going while men fight on the front. Coal mines have been a lifeline for many towns and cities in eastern Ukraine, employing tens of thousands of people and contributing significantly to the government budget through taxes.

Yulia Koba, a former child psychologist who joined the Pokrovsk mine in June as a conveyor belt operator, described it as a multipronged effort, with women in the rear supporting men on the front. “They’re there and we’re here,” she said.

Ms. Koba said male colleagues had been skeptical when she took on her new position, with some believing that women had no place in the mine’s dark and dusty tunnels. “What are you doing? Why are you here and not somewhere above ground?” she said she was asked.

But over time, Ms. Koba added, the men gradually overcame gender stereotypes and understood that women could do the job just as well as men. If women “go to serve in the armed forces, why can’t they take on traditionally male positions in the mine?” she said.

Companies have also tried to bring more women into the labor market through training programs.

The Pokrovsk mine started a program earlier this year that has so far enabled 32 women to work underground. Reskilling Ukraine, a Swedish nonprofit organization, has offered accelerated training courses for women wishing to become truck drivers. More than 1,000 women applied this year, but the organization has the funds to train only 350, said Oleksandra Panasiuk, the program coordinator.

“A lot of women wanted to be drivers, but, for a long time, society didn’t really allow them to do that,” Ms. Panasiuk said. “That’s changing.”

At the Pavlohrad mine, several women hired during the war are now hoping to make a career for themselves and move up the ladder. Ms. Yatsina, the former nanny who is now a conveyor belt operator, said she would like to become an electromechanical technician. “I’ve thought about it,” she said, a faint smile creeping onto her youthful face. “I like it here.”

Evelina Riabenko and Daria Mitiuk contributed reporting.

President Volodymyr Zelensky has said that Ukraine’s surprise offensive into western Russia, which entered its third week on Tuesday, shows the West that its fears about the ramifications of attacks on Russian territory are unfounded and should be abandoned.

As his forces attempted to push deeper into Russian territory, Mr. Zelensky seized the moment to challenge a limitation from Kyiv’s allies that has long frustrated Ukraine: the use of Western-supplied long-range weapons against Russia, which Ukraine argues is key to disrupting Moscow’s military operations.

“The whole naïve, illusory concept of so-called red lines regarding Russia, which dominated the assessment of the war by some partners, has crumbled these days somewhere near Sudzha,” Mr. Zelensky told Ukrainian ambassadors to other countries in a speech published on Monday evening. He was referring to the western Russian town of Sudzha, which Ukrainian forces captured last week.

For more than two years, Washington has prevented Ukraine from using the weapons it supplied to strike into Russia, citing fears of an escalating conflict between Moscow and the West. This spring, after months of Ukrainian lobbying, the United States and other NATO countries adjusted their policies and granted permission for Ukraine to do that.

But the Biden administration said that Ukraine could only use American weapons to strike military targets a short distance into Russia.

Mr. Zelensky confirmed in his speech to the ambassadors that Ukraine had kept its allies in the dark when preparing for the recent incursion, aware that some partners would object to an operation that “would cross the strictest of all the red lines that Russia has.”

But Moscow’s faltering response to Kyiv’s offensive — defenses near the border collapsed and reinforcements have been slow to arrive — should signal to the world that Russia is not the fearsome superpower it once appeared to be, Mr. Zelensky noted. “It is the time when the world is shedding its last and very naïve illusions about Russia,” he said.

Moscow pledged a response to Ukraine’s incursion soon after it began, but so far its military has not produced a retaliatory operation.

With its offensive, Ukraine has managed to quickly capture several settlements and one town in Russia. But so far, it appears to have failed to fulfill one of its other goals: drawing Russian units from hot spots of the battlefield in eastern Ukraine.

On Tuesday, the Russian Defense Ministry claimed that its troops had captured the eastern Ukrainian town of Niu-York, which took its name in the 19th century, a claim that could not be independently verified. The Ukrainian military said on Tuesday morning that it still held about 20 percent of the town. Niu-York and the nearby town of Toretsk, which is also under fierce Russian attack, form an important defensive belt in Ukraine’s eastern Donetsk region.

Mr. Zelensky’s remarks on Monday were some of his harshest critiques yet of Western allies. They highlight the frustration that has been building up in Kyiv, where many officials feel that Western powers, fearful of escalating the fighting, have been careful to offer just enough aid to prevent Ukraine from losing to Russia but not enough to enable it to actually win the war.

Ukraine has responded by taking bold, provocative actions to push the boundaries of Western hesitations over escalating the conflict. Kyiv has bombarded Russian cities, struck Russian oil refineries and, in the recent assault, crossed into Russia’s western Kursk region with the help of Western weapons, the largest foreign incursion in Russia since World War II.

Most of the time, Western allies who were initially hesitant eventually endorsed the moves, saying that they were acts of self-defense critical to disrupting Moscow’s military plans.

On Monday, Mr. Zelensky said Ukraine now controlled about 480 square miles of Russian territory. If confirmed, that would represent roughly the same amount of land that Russian forces seized in Ukraine from January through July of this year, according to the Institute for the Study of War, a Washington-based think tank.

The institute said on Monday night that Ukraine had continued to make marginal advances around the territory it had captured in western Russia. But Ukraine’s progress has slowed noticeably in recent days as Russian reinforcements have begun to arrive.

Military experts say that one goal of the offensive is to compel Moscow to divert troops from the front lines in Ukraine to reinforce its own border region. But so far, Russia has withdrawn only a limited number of units from the Ukrainian battlefield and instead continued to press with assaults in the contested eastern Donetsk region, according to Western military analysts and U.S. officials.

Ukraine has also had to draw on its own reserves for the cross-border attack, meaning it could be more difficult for Kyiv to respond to Russian assaults on the eastern front, analysts say.

Ukraine has been quickly losing ground near Pokrovsk, a key city in the Donetsk region, since the cross-border offensive began two weeks ago. And on Monday night, Ukraine’s General Staff said fighting was raging near the eastern towns of Toretsk and Niu-York.

Open-source battlefield maps based on combat footage and satellite images show that most of Niu-York is now under Russian control, although it remained unclear whether Russian troops had fully seized it, as Moscow claimed on Tuesday. Soldiers from the Ukrainian 53rd Brigade fighting near the town told the online news outlet Ukrainian Pravda that they still controlled about a fifth of the settlement but that the Russians kept advancing despite heavy casualties.

For now at least, Kyiv’s cross-border offensive has scored political points. It has lifted public spirits, shifted the narrative that Ukraine was slowly but steadily losing the war and given Mr. Zelensky an opportunity to press allies for more leeway.

“If our partners lifted all the current restrictions on the use of weapons on Russian territory, we would not need to physically enter particularly the Kursk region to protect our Ukrainian citizens in the border communities and eliminate Russia’s potential for aggression,” Mr. Zelensky said on Monday.

The situation on the eastern front is so dire, he added, that “any further delay by our partners in terms of long-range capabilities is becoming de facto, perhaps, the most effective support for Russia’s offensive potential.”

In Australia, he went plant hunting by helicopter and waded in crocodile-infested waters to watch a water lily bloom. In Mauritius, he grabbed a plant specimen off the ledge of a cliff. Last month, while looking for lilies in a Colombian tributary of the piranha-packed Orinoco River, he jumped from plank to plank in the pitch dark at 4 a.m. to get to a floating pontoon.

“It’s not that I am that daring,” said Carlos Magdalena, a research horticulturalist at the Royal Botanic Gardens, Kew, in London. “These situations just arise, and they are not like Superman extreme. Sometimes it’s more Peter Sellers than Indiana Jones.”

Mr. Magdalena’s main responsibility at Kew Gardens is tending tropical plants. But he is also known as “the plant messiah,” as anointed by a Spanish newspaper in 2010, for his work rescuing several plant species from the brink of extinction. That work has earned him enormous respect in the field of botany and made him somewhat of a celebrity in the horticulture world.

His renown only grew when David Attenborough, the British doyen of nature documentaries, repeated the “plant messiah” tagline at the 2012 premiere of one of his films, which featured a scene of Mr. Magdalena propagating the pygmy lily.

The attention, especially from a figure as venerated as Mr. Attenborough, initially dismayed Mr. Magdalena. “Imagine what happens when the God calls you the messiah,” he said, standing outside one of the graceful greenhouses at Kew Gardens.

It is appropriate that Mr. Magdalena’s star moment in the documentary showed him working with lilies, the plant closest to his heart and the first one he grew as an 8-year-old on his parents’ finca, a plot of land in the Asturias region of northern Spain.

The pygmy lily was what helped bring Mr. Magdalena, 51, to broader attention.

The smallest water lily in the world, Nymphaea thermarum, its flower about the size of a fingernail, had become one of Kew Gardens’ prized possessions. In 2014, it was stolen from the gardens. The thief was never caught, but Mr. Magdalena, who had cared for the tiny plant, made the media rounds, explaining the rarity of the flower, native to Rwanda.

Since then, he has embraced the role of serving as a megaphone for the silent plant kingdom, a showman as exuberant and colorful as some of the tropical flowers he cultivates.

“Plants don’t speak. Plants don’t cry. Plants don’t bleed,” he said. “So I’ve decided to speak for them.”

The youngest of five children, Mr. Magdalena was an indifferent student, but devoured his parents’ gardening encyclopedia, reading it 12 times by the time he was 8. “I preferred living with the ants,” he said of his childhood.

His mother grew flowers. His father farmed as a hobby. And nature became central to their son’s worldview. His grandfather took him around on a donkey, pointing out the names of plants and animals, and it’s a habit he inherited.

“I’ve never outgrown the stage when children point at nature,” he said.

Just as his mother would sometimes force her husband to stop the car in the middle of the road if a plant caught her eye, Mr. Magdalena can’t help but do the same, sometimes to the impatience of his Kew Gardens colleagues.

“It’s quite a sight to watch him jump into a ravine or creek looking for plants, water up to his neck, happy as can be for hours,” said Christian Ziegler, a photojournalist who has worked with Mr. Magdalena on some of his global quests to find endangered flora to nurture.

With few work opportunities in Asturias, where he managed a bar, Mr. Magdalena moved to London in 2001. If Britain was different in many ways from home, the two places shared something in common: damp, green landscapes.

At first, he took hospitality jobs. Then, one day in 2002, he visited Kew Gardens, and the trip turned into an origins story as uncommon as some of his cherished plants.

As he peered through the condensation clouding the windows of a tropical nursery, he dreamed that “all those plants could be at my disposal.”

He sent an inquiry email to Kew’s School of Horticulture, and the principal invited him for a visit. The two hit it off, and Mr. Magdalena, despite his lack of professional or academic qualifications, landed an unpaid internship.

Four months later, he earned a temporary job as assistant propagator inside the nursery of his dreams. “Time to show off,” Mr. Magdalena said.

The first plant Mr. Magdalena saved from extinction was the café marron, or Ramosmania rodriguesi, a tree that grows to about the height of a man and has distinctive white, star-shaped flowers. Endemic to the Mauritian island of Rodrigues, no living specimen had been seen since 1877 — until a schoolboy found another some 45 years ago.

A cutting was sent to Kew Gardens, and although the clone flowered, the plant did not produce seeds. Until Mr. Magdalena arrived.

In what has become part of botany lore, he spent five months intensely studying the plant. After much experimentation and 200 attempts at pollination, he succeeded in coaxing forth seeds, around 20 of which were sent to Mauritius, where the pretty flower is now seen once again.

“Carlos delivers,” said Dr. Alex Monro, a lead scientist at Kew Gardens.

While Mr. Magdalena eventually earned a diploma from the Kew horticultural school — to him, “the Oxford of gardening” — he is known for relying less on traditional techniques than for more unconventional approaches.

To help save the pygmy lily, he borrowed seeds from a botanical garden in Germany. While these seeds germinated, they quickly died. “An extinction awaiting to happen,” he said.

Mr. Magdalena tried everything, growing the seeds in acid and alkaline water, and experimenting with light and temperature. Nothing worked.

One night as he watched the water for his tortellini bubbling, he wondered if the difficulty germinating the tiny lily had to do with the amount of carbon dioxide the plants were being exposed to.

“Plants need light, water, nutrients — and they need carbon dioxide, too,” he explained.

As he prepared his dinner, he remembered that the water lilies in their native habitat in Rwanda grew in a shallow stream, and that there is much more CO2 above water than below, so he changed the depth of the water he was using in his experiment in a bid to get them more of the gas. It worked.

While his initial renown may be thanks to mini lilies, what might be his biggest accomplishment falls on the other end of the size spectrum.

Giant water lilies, of the genus Victoria, are a major part of Kew Gardens’ summer displays, displayed in a dedicated green house.

In 2007, Mr. Magdalena’s low-paid job included caring for the only two known species — Victoria amazonica and Victoria cruziana.

The plants were named after a newly crowned Queen Victoria, to secure her patronage for Kew Gardens.

As he tended to the enormous plants, Mr. Magdalena became increasingly obsessed and would spend nights researching them online, which is where he stumbled upon a photo of the strangest Victoria leaf he had ever seen and, suspecting it was an unknown species, had to learn more.

He contacted the photo’s owner, who had found this anomalously enormous lily in the Amazonian ponds of the Beni region of northern Bolivia and had transplanted cuttings from it to a man-made pond in Santa Cruz, Bolivia.

A few years later, Mr. Magdalena found himself in Bolivia, teaching a local community how to grow Brazil nuts more effectively. He took a couple days off, ventured to the man’s pond to see the mysterious, humongous lilies for himself and persuaded the owner, with an assist from the Santa Cruz Botanical Garden, to donate a few seeds to Kew Gardens.

Back in London, as the Bolivian seeds started growing with leaves and flowers that looked different from what he was used to, he began to strongly suspect he was looking at a third, unnamed species of Victoria.

He proceeded carefully in his investigation, keenly aware it was unusual in the field of botanical science that “a gardener like me,” as he said, might help identify a new species. But his observations ultimately convinced him, and the scientific community agreed.

On July 4, 2022, Kew Gardens announced the discovery of a third Victoria lily, naming it Victoria boliviana Magdalena & L. T. Sm., the second name recognizing the contribution of Lucy T. Smith, a botanist and illustrator at the gardens who had shared his conviction this was a new species.

The media attention was intense.

“I am still doing interviews. Yesterday, it was German television,” said Mr. Magdalena, who believes more giant water lily species may be awaiting discovery.

“My beloved nenúfar,” he said, using the Spanish for water lily.

Although the “plant messiah” moniker had originally bothered him as pretentious, he has since embraced it — “It’s just such a good handle” — using it as the title of a book.

“In Spain, the messiah is like being Jesus, which I am not,” he said. “For Anglos, it’s more like someone with a mission, someone who has things to say in the fight for a cause.”

His celebrity and outspokenness have not always sat well within the genteel world of gardening. But Mr. Magdalena said he doesn’t care about rubbing people the wrong way and has no plans of lowering his voice in championing the plant world, which he wants to imbue with the same charisma enjoyed by the animal kingdom.

“We need to stop thinking that plants are just greenery in the background,” he said, pointing at a blooming Titan arum. It is also known as the corpse flower, renowned as the smelliest of all plants, its rotting stench an evolutionary strategy to attract pollinators. “How cool is that?” Mr. Magdalena said.

His voice then shifted into a more serious tone, talking about the race to save as many plants as possible before they disappear forever.

“There are still more than 100,000 threatened species that are sitting at the bar having their last beer,” the former bartender said. “I have nothing else to do. Just this.”

The United States imposed sanctions against former President Michel Martelly of Haiti for drug trafficking and money laundering, according to a U.S. Treasury Department statement released Tuesday, accusing him of contributing to the destabilization and unrest afflicting the Caribbean nation.

Mr. Martelly, who served as president of Haiti from 2011 to 2016, “abused his influence to facilitate the trafficking of dangerous drugs, including cocaine, destined for the United States,” the Treasury Department said. He also “sponsored multiple Haiti-based gangs,” the statement added. The sanctions prohibit U.S. financial institutions from making loans or providing credit to Mr. Martelly.

“Today’s action against Martelly emphasizes the significant and destabilizing role he and other corrupt political elites have played in perpetuating the ongoing crisis in Haiti,” Bradley T. Smith, acting under secretary for terrorism and financial intelligence, said in the statement.

The government of Mr. Martelly, a 63-year-old popular musician known as “Sweet Micky,” was accused of rampant corruption, including misappropriation of aid worth about $2 billion from Venezuela — though he never faced any charges in Haiti.

He was sanctioned in 2022 by the Canadian government, which also accused him of profiting from armed gangs.

A United Nations sanctions report in September 2023 singled out Mr. Martelly for political corruption and gang ties. The report stated that during his presidency, he “used gangs to extend his influence in the neighborhoods in order to advance his political agenda, thus contributing to a legacy of insecurity whose effects are still being felt today.”

Haiti has been struggling with gang violence following the 2021 assassination of President Jovenel Moïse, which left a political vacuum. This year, a coordinated offensive by armed gangs in the capital, Port-au-Prince, led to the collapse of the government and the appointment of a transitional council in April and an interim prime minister in May.

About 400 Kenyan police officers have so far deployed to Haiti this summer after the United National authorized a Multinational Security Support mission, largely funded by the United States, to assist the undermanned local police in restoring law and order and security

The gangs still control large swaths of the capital, parts of which resemble a war zone where civilians are victims of murder, rape and kidnapping for ransom. There were 547 victims of killings and injuries in gang-related violence in July alone, according to the U.N. That represented a 35 percent increase since the arrival of the Kenyan-led force.

There has also been an increase in sexual and gender-based violence, as well as the growing use of children by gangs to carry out criminal activities, according to Cluster Protection Haiti, a joint Haitian and U.N. effort to tackle threats to civilians.

The United States has placed sanctions on gang leaders and politicians, including one former prime minister, but Mr. Martelly, the former president who handpicked Mr. Moïse as his successor and held substantial sway over his administration, is the most high-profile Haitian official to appear publicly on any sanctions list.

Former Prime Minister Laurent Lamothe of Haiti was sanctioned by the United States in June 2023 for the alleged misappropriation of $60 million in Haitian public funds. Mr. Lamothe had been living in Miami but is not a U.S. resident. He left the United States at some point and has not been allowed to return since the sanctions were announced.

It was unclear whether the sanctions would affect Mr. Martelly, who is a U.S. resident and lives in Miami, according to his Florida lawyer, Richard Dansoh, who said he was taken by surprise by Tuesday’s news.

“It came out of the blue,” said Mr. Dansoh, adding that Mr. Martelly recently hired an attorney specializing in sanctions to help monitor his possible legal exposure in the United States. Mr. Dansoh said he had not spoken to his client yet. He said he had spoken to Mr. Martelly’s wife, Sophia Martelly, who was in a state of shock. “She is wondering what the next steps are,” he said.

Deep-sea divers with Italy’s firefighter corps resumed their search on Tuesday for six missing passengers — including a British software mogul and his daughter — of a yacht that sank off the coast of Sicily the previous day.

Twenty-two people were on board the 180-foot British-flagged sailing yacht, the Bayesian, which was anchored near the port of Porticello, when it was hit by what witnesses described as a waterspout, a small tornado on water, during a sudden and violent storm.

Fifteen people who managed to get to a raft were rescued by the captain of a nearby sailing cruise ship. The body of the yacht’s cook, identified by news outlets as Recaldo Thomas, a Canadian Antiguan, was recovered on Monday. But several people are still unaccounted for, according to Salvatore Cocina, an official with Sicily’s civil protection agency.

Those still missing are Mike Lynch, a British technology entrepreneur; his daughter Hannah; Jonathan Bloomer, chairman of Morgan Stanley International; his wife, Judy Bloomer; Christopher J. Morvillo, a lawyer at Clifford Chance; and his wife, Neda Morvillo.

Mr. Lynch was acquitted of fraud in a U.S. trial in June, ending a high-profile, decadelong legal battle against accusations that he had defrauded Hewlett-Packard when he sold his company, Autonomy, to Hewlett for $11 billion.

Mr. Lynch and the others went missing days after Mr. Lynch’s co-defendant at the fraud trial, Stephen Chamberlain, a former vice president of finance at Autonomy, was fatally struck by a car on Saturday while out for a run, his lawyer, Gary S. Lincenberg, said in a statement.

Prosecutors in the Italian city of Termini Imerese, east of where the yacht sank, are opening a formal investigation into the yacht’s sinking. Reached by telephone, the chief prosecutor declined to comment.

The search for the missing passengers began on Monday but was suspended late that night as crews found themselves limited to the bridge deck and items like furnishings “obstructing passage,” the firefighters’ corps wrote on social media.

When divers resumed the search on Tuesday, ships trawled the waters near the site, the corps said in a statement. The Italian Coast Guard also said in a statement that search operations were “continuing unabated,” with the deployment of helicopters. There was no evidence that gasoline was leaking from the yacht, the Coast Guard said.

The yacht was lying on its right side in about 165 feet of water, meaning that divers, working in pairs, could stay underwater for only about 12 minutes at a time, said Luca Cari, a spokesman for the firefighters’ corps.

Divers were seeking a safe point of access to the vessel’s cabins. “Obviously, everything fell and the space is very tight,” Mr. Cari said, adding that the divers were having to remove obstacles, like furnishings and electrical wiring, that were “completely blocking passages.”

The firefighters’ corps said in a statement that it was impossible to verify whether people were inside the hull.

Mr. Cari said that several divers had been part of the search-and-rescue operations when the Costa Concordia, a cruise liner, capsized off the Tuscan island of Giglio in 2012, killing 32 people. It is considered one of the worst maritime disasters in modern Italian history.

“It’s like the Costa Concordia, but much smaller,” Mr. Cari said in a telephone interview, comparing the search operations. “In the Costa Concordia, we came across many obstacles but we somehow were able to overcome them. Here, the obstacles block the passages and have to be removed.” He added, “This makes it more difficult.”

Crews were also trying to raise the yacht, which experts will examine to try to determine why it sank. Until then, experts can only hypothesize what happened.

Karsten Borner, the captain of a ship, the Sir Robert Baden Powell, which picked up the Bayesian’s 15 survivors, said in an interview that when the wind picked up around 4 a.m. Monday, the Bayesian was about 490 feet behind his vessel. Once the wind wound down, he said, he could not see the yacht anymore.

“My theory was that she was capsized first and then went down over the stern,” Mr. Borner said.

Dario Boote, a ship structures and naval architecture professor at the University of Genoa, said: “Now I imagine that a whole series of lawsuits will be triggered, obviously to ascertain whether there is any responsibility, as always happens very unpleasantly in these situations.” He said, however, that in this case, responsibility might be hard to determine. “Clearly, only once the wreck is raised will we know more,” he added.

Several fishermen told Italian news outlets that they had witnessed a waterspout. Peter Inness, a meteorologist at the University of Reading, said they were relatively common in the Mediterranean, though their occurrence and intensity are unpredictable.

“Until one actually forms, you can’t start telling people where it is,” Mr. Inness said, or “how to get out of the way.”

The inclement weather — with lightning intermittently streaking through the sky — made it hard to know exactly why the yacht sank. Col. Attilio Di Diodato, director of the Italian Air Force’s Center for Aerospace Meteorology and Climatology, said the agency had registered intense lightning activity and strong gusts of wind in the area at the time the boat sank.

The Bayesian had one of the tallest aluminum masts in the world, according to its builder, Perini Navi. “Having a tall aluminum mast would not make it the safest port to be in case of a storm,” said Andrea Ratti, associate professor of nautical design and architecture technology the Politecnico di Milano. The type of intensity unleashed by a violent lightning storm “could have created a significant shock wave,” he added.

He, too, cautioned that “a lot of questions will remain until we have other elements at our disposal.”

Modern yachts are built to withstand meteorological events of reasonable intensity, and all international naval registers suggest that new ships be designed for higher waves and more frequent and extreme weather events.

But “this seems a case of an unreasonable extreme event,” said Emilio Fortunato Campana, an expert in Naval Hydrodynamics at Italy’s National Research Council. “In that case, no ship is 100 percent safe,” he added. “I think the Titanic showed that nothing is unsinkable.”