The fates of two men key to Putin’s war are now both in question.

On Wednesday, Russian state media reported that the general had been demoted, and that the mercenary was listed as a passenger on a plane that crashed, killing everyone on board.

Wednesday’s fast-moving developments in Russia suggested that the end had come, in different ways, for two men who had proved pivotal over the past year to Russia’s war effort. If Mr. Prigozhin is confirmed to have been killed and General Surovikin remains sidelined from the invasion, questions are sure to be raised over whether President Vladimir V. Putin can sustain his fight without two of his most effective — and most brutal — military leaders.

The war itself has been a grinding slog for both sides.

Nearly three months into their counteroffensive, Ukrainian forces are still struggling to recapture territory occupied by Russia. American officials blame, among other things, Kyiv’s continued focus on Bakhmut, the city into which Mr. Prigozhin poured thousands of fighters recruited from Russian prisons for one of the bloodiest battles of the war.

Russian forces, too, have made little gains since taking Bakhmut. Analysts say that those troops are increasingly exhausted as they defend against Ukraine’s onslaught, and that Mr. Putin might well be forced to declare another draft of civilians to replenish the invading army’s ranks.

In July, William J. Burns, the C.I.A. director, said that a “complicated dance” with Mr. Putin had developed. Mr. Prigozhin continued to travel between Russia and Belarus, where President Aleksandr G. Lukashenko had offered Mr. Prigozhin and his fighters refuge, and other locations. But Mr. Burns predicted that Mr. Putin would move against Mr. Prigozhin, who staged the most significant challenge to Mr. Putin’s authority in decades with his rebellion.

“Putin is someone who generally thinks that revenge is a dish best served cold,” Mr. Burns said at the Aspen Security Forum in Colorado last month. “So he’s going to try to settle the situation to the extent he can. But, again, in my experience, Putin is the ultimate apostle of payback. So I would be surprised if Prigozhin escapes further retribution for this.”

U.S. officials have said that Russia continues to depend on the Wagner mercenary group, particularly for its operations in Africa, a relationship that could have offered Mr. Prigozhin some insurance. But Russia was no longer dependent on the private forces in Ukraine, a reality that potentially gave Mr. Putin a broad hand, other officials noted previously.

On Wednesday, Russian media announced the ouster of Gen. Sergei Surovikin. U.S. officials said General Surovikin had at least known about Mr. Prigozhin’s planned mutiny and may have supported it. As a result, General Surovikin had lost his command, and was under some sort of movement restrictions, if not formal detention, U.S. officials confirmed Wednesday, shortly before the news of the crash became public.

After the announcement of General Surovikin’s removal, American officials noted that they were surprised by how Mr. Prigozhin continued to appear relatively free, recently traveling to Africa and posting a video on social media. In contrast, General Surovikin had lost his freedom of movement, a U.S. official said.

Through a vast network of shell companies and intermediaries, Mr. Prigozhin’s activities have included catering, producing action movies, making beer and vodka, cutting timber, mining diamonds and hiring people to sow disinformation in elections abroad, including the 2016 U.S. election.

The exact size of his business has been shrouded in mystery and the fate of his sprawling empire is uncertain.

After Mr. Prigozhin led a short-lived mutiny in June, The New York Times took a look at his business interests around the world.

October 2022

Mr. Prigozhin was one of two powerful supporters of Mr. Putin to publicly turn on Russia’s military leadership after it ordered a retreat from Lyman, a key city in eastern Ukraine, emphasizing that the retreat was a major embarrassment for the Kremlin.

November 2022

Just a day before the U.S. midterms, Mr. Prigozhin sardonically boasted that Russia was interfering in the election.

February 2023

Mr. Prigozhin accused two Russian military leaders of treason in a series of hostile audio messages. He claimed that the Russian defense minister, Sergei K. Shoigu, and its most senior general, Valery V. Gerasimov, were withholding ammunition and supplies from his fighters to try to destroy Wagner.

May 2023

Mr. Prigozhin issued a series of inflammatory statements. He once again accused Russia’s military bureaucracy of starving Wagner forces of necessary ammunition and threatened to withdraw them from Bakhmut. Days later, he appeared to backtrack on that threat after saying he had been promised more arms.

June 2023

Mr. Putin mobilized Russian troops to defend Moscow from what he called an armed rebellion by Mr. Prigozhin, whose forces had claimed control of Rostov-on-Don and were seen moving north along a highway toward the Russian capital. Then, in a surprise turn of events, the Belarusian president, Aleksandr G. Lukashenko, said he had secured Mr. Prigozhin’s agreement to halt his forces’ advance. Mr. Prigozhin turned his forces around.

The Kremlin’s spokesman, Dmitri S. Peskov, said that Mr. Prigozhin would flee to Belarus, and that Russia’s military operations in Ukraine would continue unchanged.

July 2023

Mr. Lukashenko told reporters that Mr. Prigozhin was a “free man” currently in St. Petersburg, adding that he “maybe” went to Moscow and was not in Belarus. A Pentagon official who spoke on the condition of anonymity because of the sensitivity of the situation later confirmed that Mr. Prigozhin had been in Russia, between Moscow and St. Petersburg, during most of the period since the mutiny.

Unverified photographs circulated on social media suggested that Mr. Prigozhin was meeting with African officials in St. Petersburg, where some of the continent’s top leaders had converged for a summit with Mr. Putin.

August 2023

Mr. Prigozhin emerged in an unverified video message posted on Telegram channels affiliated with his Wagner forces, appearing to recruit for the group’s operations in Africa. On Wednesday, Gen. Sergei Surovikin, was demoted from his post as chief of the air force, according to Russian state media. The country’s former top commander in Ukraine, he is the only senior official with ties to Mr. Prigozhin that has been demoted or punished following the rebellion’s aftermath.

“An investigation has been launched into the crash of the Embraer aircraft, which occurred tonight in the Tver region,” Russia’s Federal Air Transport Agency said, Tass reported. “According to the list of passengers, among them is the name and surname of Yevgeny Prigozhin.”

The Embraer jet was traveling from Moscow’s Sheremetyevo Airport to St. Petersburg, Russia, and crashed less than 30 minutes after takeoff, Tass said.

Mr. Prigozhin, an outspoken tycoon, built the private paramilitary force that has fought on Russia’s behalf in Ukraine and across Africa. Frustrated over the country’s military leadership, he instigated a short rebellion two months ago, a mutiny that posed a grave threat to the government of President Vladimir V. Putin.

The Russian Ministry of Defense said on Tuesday that one of its fighter jets had “successfully hit” a high-speed Ukrainian military boat carrying troops around 26 miles east of Snake Island. It published a video that appeared to show a vessel trying to perform sharp S-shaped turns to evade fire from an aircraft overhead.

On Wednesday, Ukraine’s military intelligence service acknowledged the attack but said that it had failed. In a statement posted on the Telegram messaging app, the department said that Ukrainian forces had come under a failed attack and had struck back, firing a missile from a warship that “damaged the Russian aircraft, which was forced to immediately leave the scene.”

The Ukrainian department’s video of the incident appeared to show several combat boats near an oil platform performing the same S-shaped turns visible in the footage released by the Russian Ministry of Defense.

In the Ukrainian video, a white streak can be seen descending toward the sea and disappearing into it, which Ukrainian forces claimed was a Russian missile falling into the water. Ukraine said that no casualties had been reported. The video then shows one of the combat boats firing a missile upward, but does not show whether it hit any target.

Ukraine did not comment on another Russian claim on Tuesday that it had struck a Ukrainian reconnaissance vessel.

Tensions have risen in the Black Sea since last month, when Moscow announced it was terminating a deal that ensured a safe passage of Ukrainian grain across the Black Sea. Since then, clashes in the area have intensified, with Russia striking at Ukrainian Black Sea ports and Ukraine retaliating by targeting Russian ships, in what appears to be a battle for control of the sea.

The attacks, none of which could be confirmed independently, appeared to be the latest in a series of strikes by Russian forces on civilian targets since Moscow launched its full-scale invasion of Ukraine almost 18 months ago. The United Nations has recorded the killings of about 9,500 civilians in that time, but notes that the actual figures may be “considerably higher.”

Ihor Klymenko, Ukraine’s minister of internal affairs, said the attack on the school on Wednesday came at 10 a.m., in the northern city of Romny, in Sumy region, about 60 miles southwest of the Russian border.

Four people who were walking past the school at the time of the strike were injured, he said in a post on the Telegram messaging app, noting that some residents had not heeded warnings to take shelter. He did not elaborate.

Mr. Klymenko posted photographs that he said showed the aftermath of the missile strike. One shows rescue workers crawling through the rubble of a building. Another shows emergency workers carrying a corpse wrapped in a white plastic sheet away from the building’s wreckage.

Ukrainian regions close to the Russian border and areas near to the front line have borne the brunt of Moscow’s strikes. One frequent target is Kherson, a southern region where Ukrainian forces regained partial control last fall.

Six people were injured in the Kherson region on Wednesday when Russian forces dropped two guided bombs on a kindergarten and residential buildings before dawn, said ​​Oleksandr Prokudin, head of the regional military administration.

“The bombing caused a fire,” he said on Telegram, adding that it had since been extinguished.

Three residents of the village of Torske in Donetsk region died in Russian shelling on Tuesday, according to Pavlo Kyrylenko, the head of the regional military administration. The village is a few miles east of Lyman, a town taken by Russian forces last May and then recaptured by Ukraine in the fall. It now lies close to a frontline in the east of the country.

“Russian fortifications in Ukraine are the most extensive defensive works in Europe since World War II,” military analysts wrote in a paper released in June by the Center for Strategic and International Studies, or C.S.I.S., noting that they extended over some 1,000 kilometers, or about 620 miles.

General Surovikin was appointed as commander of Russia’s forces in Ukraine last October before being relieved of that job in January. Many trenches and fortifications were built during that time, satellite radar data shows.

“It strongly appears that he ramped up the constructions of fortifications while he was commander of Russian forces in Ukraine,” said Seth Jones, one of the authors of the C.S.I.S. report, noting that General Surovikin had accurately gauged the advantages of fighting from a defensive position as Kyiv prepared to launch its counteroffensive.

The C.S.I.S. report said that the biggest defenses were built in the southern Zaporizhzhia region, where Ukrainian forces have been struggling to recapture territory in recent weeks. The Zaporizhzhia defensive system consists of several layers of trenches, barriers and artillery positions that run more than 10 kilometers deep, it said.

Russia has also installed miles-long rows of concrete pyramids known as dragon’s teeth to slow Ukrainian vehicles and force them into preset positions where Russian forces can target them.

The Ukrainian military appeared to have broken through a first line of defense when its forces entered the small village of Robotyne, in the Zaporizhzhia region, this week. But farther to the south lie two other defensive lines made of trenches and anti-tank traps that stand in the way of efforts to reach the larger city of Tokmak.

General Surovikin was also credited with withdrawing Russian forces from the southern city of Kherson fairly successfully last fall, when they were nearly encircled and cut off from supplies. U.S. officials concluded that based on communications intercepts, General Surovikin represented a hard-line faction that wanted to use the toughest tactics against Ukrainians.

Moscow launched its unprovoked full-scale invasion of Ukraine almost 18 months ago, but the Kremlin has sought to portray the decision as a defensive move against a hostile Ukrainian government, and antagonism from the United States, Europe and NATO.

“Our actions in Ukraine are guided by only one thing — to put an end to the war that was unleashed by the West,” Mr. Putin added, according to an English translation of the live video stream of his address provided by the South African Broadcasting Corporation, in a familiar refrain.

Mr. Putin is the only leader of a BRICS nation not to attend the summit in Johannesburg in person this week because he is wanted for war crimes under a warrant issued by the International Criminal Court. South Africa, which is a party to the treaty that created the court and would have been obliged to arrest him if he had traveled there, had asked him to stay away.

The summit has focused on whether to expand the club and how to be a counterweight to Western powers. The war in Ukraine, the prospect of a major BRICS expansion and heightened tensions between China and the United States have drawn unusual attention to the meeting.

BRICS members have seen it as the kernel of a diplomatic and economic bloc to counterbalance Western-dominated alliances like the Group of 7. Dozens of other countries have expressed interest in joining, and Saudi Arabia, Indonesia, Egypt and Argentina are among those considered to be at the top of the list.

For China’s top leader, Xi Jinping, the summit has offered an opportunity to cast himself as a leader of the developing world. Beijing’s support for Russia and its aggressive posture on issues like the status of Taiwan, the self-governed island Beijing claims as its territory, have alienated it from countries in North America, Europe and Asia.

In China’s escalating rivalry with the United States, Africa is an emerging battleground for global influence. Beijing has invested billions in countries that have long been ignored by the West. The result of that outreach has been diplomatic support in international organizations like the United Nations and access to critical minerals needed to power growing industries, like electric vehicles.

While not mentioning it by name, Mr. Xi took aim at the United States on Tuesday, painting it as a bully and a threat to peace in a speech that was read by China’s commerce minister, Wang Wentao, for undisclosed reasons.

In his speech to the summit on Wednesday, President Luiz Inácio Lula da Silva of Brazil said the war in Ukraine had exposed “the limitations” of the U.N. Security Council and distracted from other crises deserving of global attention.

At the same time, BRICS countries had risen to the challenge of seeking to bring peace in Ukraine, Mr. Lula said, singling out efforts by Brazil, China and South Africa. The three countries have tried to maintain good relations with Russia despite the war.

Mr. Kiper posted what he said were photographs of the aftermath of the attack. One showed the corrugated iron roof of a warehouse twisted and hanging to the ground, and another showed the interior of a warehouse with its roof shattered and exposed to the sky. Heaps of grain were in one corner. Mr. Kiper did not give a precise location for the attack.

The strike is another blow to Ukraine’s ability to export grain through its Danube River ports, after recent attacks on the port of Reni and the port of Izmail.

For years, Ukraine’s Danube ports played a secondary role as a conduit for the country’s grain exports to its Black Sea ports such as the one in the city of Odesa. But they have become increasingly vital since Moscow, whose navy dominates the Black Sea, pulled out of a deal last month that allowed Ukraine to export its grain and other food crops via Turkey.

Dozens of cargo vessels are waiting off the Romanian Black Sea port of Sulina, and some are set to navigate a canal that leads to Ukraine’s Danube ports, the global maritime data provider MarineTraffic website showed on Wednesday.

Since Moscow ended the grain deal, Russian forces have repeatedly struck the port of Odesa, as well as other facilities connected to Ukraine’s grain industry. Ukraine is a major exporter of grain and the crop plays an important role both in global wheat markets and in the country’s economy.

At the same time, there have been a series of episodes in the Black Sea, including a Ukrainian attack by sea drones on the Kerch Strait Bridge, which connects Russia with the Crimean Peninsula, an attack on a Russian warship and the interception by Russia’s Navy of a cargo vessel, during which warning shots were fired.

Some Wagner fighters have relocated to Belarus, where officials have said the mercenaries are training Belarusian troops; others remain active in the Central African Republic, Mali and elsewhere in Africa, where they have helped prop up authoritarian leaders loyal to Moscow.

Mr. Prigozhin on Monday released a brief video message online for the first time in the mutiny’s aftermath, hinting that he was in Africa, even though the video recording’s timing and location were unclear. Dressed in fatigues and holding an assault rifle, he said that Wagner was “making Russia even greater, on all continents, and Africa even more free.”

General Surovikin has not been seen in public since the rebellion and his whereabouts has remained a mystery. In July, Andrei Kartapolov, the head of the defense committee of Russia’s lower house of Parliament, said that General Surovikin was “taking a rest” in response to questions from a reporter.

On Wednesday, RIA Novosti, a Russian state news agency, said that “the ex-commander in chief of the Aerospace Forces of Russia, Sergei Surovikin has now been relieved of his post.” It said that Col. Gen. Viktor Afzalov, chief of the air force’s general staff, had been named as the acting commander.

“Surovikin was relieved of his post in connection with the transfer to another job. He is now on a short vacation,” the RIA report added, citing a report from the Russian news outlet RBC.

Analysts have described General Surovikin, called “General Armageddon” for his ruthless tactics, as a brutally effective leader in a Russian military that even many Russian cheerleaders of the war have described as troubled by incompetence in its command structure. But his links to Mr. Prigozhin’s Wagner mercenary group, which took over a Russian city and began a march on Moscow in its brief mutiny, appeared to precipitate his fall from grace.

U.S. officials believe that General Surovikin had advance knowledge of Mr. Prigozhin’s rebellion. In the hours after the mutiny began, the Russian authorities quickly released a video of the general calling on the Wagner fighters to stand down.

Rumors have been circulating among Russia’s military bloggers, some of whom have close ties to Russian officials and the military, that General Surovikin had been under house arrest since the failed mutiny.

The reports about General Surovikin’s firing are “far from news for people in the know,” wrote Mikhail Zvinchuk, a popular pro-war Russian blogger who posts under the moniker Rybar on the messaging app Telegram. He added that General Surovikin lost his job immediately after Mr. Prigozhin’s rebellion.

General Surovikin was appointed to lead what Russian officials describe as its “special military operation” in Ukraine in October 2022 before being relieved of that job in January. In 2015, he commanded Russia’s forces during the country’s intervention in Syria, and he was the head of the Russian air force from 2017 onward.

In his three-month stint as the commander of Russian forces in Ukraine, General Surovikin helped stabilize Russia’s flailing war effort. In the fall, he oversaw what analysts described as a professionally managed withdrawal of Russian troops from the southern Ukrainian city of Kherson, where they were nearly encircled last fall and cut off from supplies.

He is also believed to have spearheaded the construction of Russia’s daunting network of defensive lines in the territory it occupies in Ukraine, which have challenged Kyiv’s counteroffensive.

General Surovikin’s replacement, General Afzalov, has been chief of the Air Force’s general staff since 2018, according to Russian state media, having risen through the ranks. He was “directly involved in planning and organizing” the full-scale invasion of Ukraine, according to Anton Gerashchenko, an adviser to Ukraine’s Interior Ministry, in a post on the social media platform X, formerly known as Twitter.

General Afzalov had previously served as the interim commander of Russia’s air force while General Surovikin led Russia’s armed forces in Ukraine. Suspicions that General Afzalov had replaced General Surovikin were raised in July, when the former was shown in official video footage delivering an air force report to General Valery V. Gerasimov, Russia’s top military officer.

Drone attacks deep in Russian territory have become more frequent as Ukraine wages a counteroffensive, which has been bogged down by what U.S. and other Western officials say is a misallocation of troops.

In the Russian capital, drones damaged a building under construction in a gleaming skyscraper complex known as Moscow City, which has been hit at least three times in the past month.

The deadly assault on Lavy, a village in the Belgorod region near the border with Ukraine, was the latest in near-daily attacks on the area that have killed at least six others this summer, according to Russian officials. Since Moscow launched its full-scale invasion almost 18 months ago, Ukrainian forces have regularly fired on villages in the region, according to the regional governor, Vyacheslav Gladkov.

The claims have not been independently verified.

Two other drones were shot down early Wednesday in suburban districts of the Moscow region, the Russian Defense Ministry said on the messaging app Telegram. According to the ministry, the drone that struck Moscow City was electronically jammed and lost control before crashing into the building.

Ukrainian officials did not immediately comment on the episodes, as has been their practice on attacks inside Russia. Asked about the attacks, a representative for the U.S. State Department said that it didn’t encourage them but that “it’s up to Ukraine to decide how to defend itself.”

“Russia started this unprovoked war against Ukraine,” the representative said. “Russia could end it at any time by withdrawing its forces from Ukraine instead of launching brutal attacks against Ukraine’s cities and people every day.”

The stepped-up attacks near the center of power in Moscow have been seen as an attempt to bring the war in Ukraine home to Russia and its citizens. The drone attacks in the Moscow region have not caused injuries or deaths, according to Russian officials.

Built mostly during President Vladimir V. Putin’s time in power, Moscow City has been held up as a symbol of the modernization of Russia’s economy. It houses government ministries as well as finance and tech companies.

Russia’s Federal Agency for Air Transport said that air traffic had been temporarily halted Wednesday morning at nearby airports for safety reasons and that at least two flights had been diverted.

Also early on Wednesday, Russian forces attacked the southern part of Ukraine’s Odesa region with drones, damaging shipping facilities including granaries, according to the regional Ukrainian military administration. Russia has for weeks been targeting Ukraine’s grain export infrastructure after pulling out of the internationally brokered Black Sea grain deal in July. The claims had not been independently verified.

Juston Jones and Edward Wong contributed reporting.

But Ukrainian forces have sustained heavy casualties, and progress has been slowed by dense minefields, tank traps, withering air assaults and artillery bombardments.

THE LATEST: The Ukrainian military said Tuesday that its troops had entered the small southern village of Robotyne “with a fight,” a sign that Kyiv’s counteroffensive continues to inch forward in the face of stiff Russian resistance.

While Robotyne did not appear to be fully back under Ukrainian control, the deputy defense minister, Hanna Malyar, said that soldiers from Ukraine’s 47th Mechanized Brigade had entered the village and “organized the evacuation of civilians” on Bradleys, American-made fighting vehicles supplied by the United States. The brigade is one of the three Western-equipped and trained units that were deployed early in the campaign.

“In response, the Russians are continuously shelling Robotyne with artillery,” she said in a post on the Telegram messaging app. “The fighting continues.”

Ms. Malyar had said on Monday that Ukrainian forces had advanced to the southeast of Robotyne and also to the north of the settlement of Mala Tokmachka, which is around six miles to the northeast. Russia’s Ministry of Defense said on Tuesday that its troops had repelled a Ukrainian assault near Robotyne.

There was no independent confirmation of the claims by either side.

WHY IT MATTERS: Robotyne, in the Zaporizhzhia region of southern Ukraine, lies along the Ukrainian forces’ line of attack in the direction of Melitopol.

Though the village is little more than a speck on the map, Ukrainian forces, using tanks and armored vehicles supplied by the country’s NATO allies have been held up for weeks by dug-in Russian forces and minefields.

The Institute for the Study of War, a Washington-based research organization, had said this month that Ukrainian forces’ “ability to advance to the outskirts of Robotyne — which Russian forces have dedicated significant effort, time and resources to defend — remains significant even if Ukrainian gains are limited at this time.”

If Ukraine manages to push through Robotyne, it could open up new opportunities in its continuing offensive. Russian forces might not have been able to properly reinforce their defenses in time, which could give Kyiv the chance to exploit its recent gains.

But no matter the battle’s outcome, every inch of Russian-held territory is still staunchly defended by obstacles erected to slow the Ukrainian advance and further rings of Russian entrenchments.