It was a tense conversation between two authoritarian leaders accustomed to getting their way.

President Vladimir V. Putin of Russia was offering explanations for the Azerbaijan Airlines plane crash that had killed 38 people days earlier. Perhaps it was a flock of birds, Mr. Putin said, or an exploding gas canister. Maybe a Ukrainian drone.

But President Ilham Aliyev of Azerbaijan was not buying it, according to two people familiar with that late December phone call. It had become clear within hours of the crash that the plane had been shot down by Russian air defenses in what appeared to be a lethal mistake. It left shrapnel lodged in the leg of one passenger and riddled the fuselage with holes.

On Dec. 29, Mr. Aliyev went public with his anger without mentioning the Russian president by name. “Attempts to deny obvious facts,” he said, “are both nonsensical and absurd.”

The people who described the phone call insisted on anonymity to discuss sensitive diplomatic communications. The Kremlin did not respond to a request for comment.

The furor over the plane crash — and Mr. Aliyev’s willingness to challenge Mr. Putin in public — has revealed a remarkable breach between two post-Soviet rulers who had become close over more than two decades in power. Mr. Putin tried to enlist Mr. Aliyev in an apparent effort to keep quiet the cause of the crash; Mr. Aliyev, emboldened by Russia’s weakened influence in lands it once dominated, insisted that Russia publicly recognize its guilt.

Interviews last week with Azerbaijani officials and people close to the government showed how the Dec. 25 crash of an Embraer 190, with 67 people aboard, has become a geopolitical milestone for the former Soviet Union. Rather than allowing Mr. Putin to dictate his response to the tragedy, Mr. Aliyev has repeatedly lashed out at Russia over its failure to accept responsibility.

Rasim Musabekov, a member of the Azerbaijani Parliament’s foreign affairs committee, described Russia’s response to the crash as “an absurd attitude.”

“Azerbaijan will not accept such a chauvinist attitude,” he added.

Behind the scenes, the interviews showed, those tensions flared directly between Mr. Aliyev and Mr. Putin, even though the two autocrats have often found common ground. In the call on Dec. 28 and another the next day, the people familiar with the calls said, Mr. Putin urged Mr. Aliyev to agree to have a Moscow-based aviation body investigate the crash. Mr. Aliyev refused, insisting that the plane’s black boxes be decoded in Brazil, where the jet was made, a striking display of mistrust of the Russian leader.

Officials in Azerbaijan’s capital, Baku, arranged interviews for The New York Times with three survivors, who said it became clear to some passengers that they were under attack immediately after at least two explosions rocked the plane in midair.

After the second blast, a girl started screaming. Leyla Omarova, 28, looked across the aisle from her window seat and saw the girl’s tights stained with blood.

Three rows behind them, Nurullah Sirajov, 71, had been trying to comfort his wife. The first bang must have been the landing gear, he’d told her. They had never flown before.

Then came the second explosion, a rush of wind from the back of the plane and yells, he said, from other passengers: “They hit us.”

As the jet jerked up and down, coming within 100 feet of the Caspian Sea, Mr. Sirajov thought that at least his and his wife’s marital squabbles over who would die first would finally be resolved: They would die together. But after the front part of the plane disintegrated on impact, the tail section broke off, turned over and slid hundreds of yards through the sandy soil.

“Anyone alive?” Mr. Sirajov remembers yelling in the sudden silence as he dangled upside-down from his seatbelt.

Because Europe closed its airspace to Russia after Mr. Putin’s invasion of Ukraine, many Russians flying westward now connect in Azerbaijan, an oil-and-gas-rich former Soviet republic of 10 million sandwiched between Russia and Iran. Russia also sees Azerbaijan as a key link in an expanded trade route south to Iran, India and the Persian Gulf.

Its role as a transit point for a Russia beset by sanctions is just one way that Azerbaijan has seen its leverage rise against its far larger northern neighbor. Mr. Aliyev has also taken advantage of the Russian military’s distraction in Ukraine to push Russian peacekeeping troops out of Nagorno-Karabakh, the Armenian-controlled enclave that Azerbaijan recaptured in 2023.

Mr. Aliyev has solidified his country’s alliance with Turkey and armed Azerbaijan with high-tech weapons purchased from Israel. He has waged a fierce crackdown against activists and independent journalists, but has maintained a relationship with Europe, which sees Azerbaijan as a key alternative to Russian oil and gas.

Farhad Mammadov, a political analyst in Baku, said that Russia’s political and economic “levers of pressure” on Azerbaijan had been reduced to “practically none.” Aykhan Hajizada, the spokesman for Azerbaijan’s Foreign Ministry, was blunt in arguing that his country had leverage over Russia: “They don’t want to lose Azerbaijan as well,” he said.

The uproar over the plane crash has emerged as a test case. A senior American diplomat, speaking on condition of anonymity because he was not authorized to comment publicly, described the fallout from the crash as “a proof of concept” for Azerbaijan’s ability to stick up for itself. Other post-Soviet countries that have also sought a more arm’s-length relationship with Russia, like Kazakhstan, are watching closely.

“If this is how you behave in this incident with Azerbaijan, then what will the Uzbeks, the Kazakhs and the other remaining partners of Russia think of you?” Mr. Musabekov, the member of Parliament, asked. “It’s that Russia, as a state, is a very, very toxic partner that you need to minimize relations with.”

Mr. Aliyev, who studied in Moscow and took over as Azerbaijan’s ruler from his father in 2003, learned about the crash while en route to a summit of post-Soviet leaders in St. Petersburg. He called Mr. Putin from the plane to tell him he was not coming.

Hours later, Azerbaijani officials landed in Aktau, Kazakhstan, the airport where the Embraer 190 had tried to make an emergency landing. At the crash site nearby, the officials immediately realized that the theories of a bird strike or exploded oxygen canister that they had been hearing from Russia were wrong.

“When I saw the aircraft, it was riddled with holes,” Rinat Huseynov, the safety director for Azerbaijan Airlines, said in an interview. “We didn’t imagine that this was possible at all.”

Mr. Aliyev and Mr. Putin spoke again twice in the days after the crash. Mr. Putin apologized for the “tragic incident” happening in Russian airspace but did not acknowledge that Russia had shot down the plane. The day after the apology, on Dec. 29, Mr. Aliyev went public to accuse Russia of a cover-up.

“Unfortunately, for the first three days, we heard nothing from Russia except for some absurd theories,” Mr. Aliyev said.

Officials said they expected preliminary findings from the investigation by the end of January. Mr. Aliyev reiterated last week that Russia needed to accept responsibility and pay compensation, while the Kremlin said it was cooperating with the probe.

“We are interested in an absolutely objective and unbiased investigation,” Dmitri S. Peskov, Mr. Putin’s spokesman, told reporters last week.

The Azerbaijanis’ working theory is that the shrapnel from exploding missiles of a Russian Pantsir air-defense system damaged the plane. Metal fragments as large as four inches long were found at the crash site.

The flight data and cockpit voice recorders, officials said, could help explain why the pilots chose to cross the Caspian Sea to land in Kazakhstan rather than at a closer airport in Russia; Mr. Huseynov, the airline safety director, said the decision appeared logical given the cloudy conditions in southern Russia at the time.

Inside the passenger cabin, the flight attendants were trying to calm the panic. Ms. Omarova, en route to see family in Russia, said she lost consciousness. Mr. Sirajov, who had packed New Year’s presents for grandchildren in Grozny, said all he could think about was comforting his wife.

Flight data shows that after crossing the Caspian Sea, more than an hour after the pilots reported what they thought was a bird strike, the plane crashed on a second attempt to land at Aktau airport. All of the survivors were sitting in roughly the rear third of the plane, according to a person close to the investigation.

After the tail section came to a stop, Mr. Sirajov fumbled in the darkness to open his seatbelt, unable to tell what had happened to his wife. Only later did he learn that she had also survived.

Finally, Mr. Sirajov yanked his belt open and tumbled onto the cabin’s ceiling. “Go that way, go that way,” he recalls hearing as someone pushed him toward a sliver of light.

Poland’s prime minister appeared on Wednesday to confirm the conclusions of Western intelligence officials who had warned of a Russian plot to blow up cargo aircraft over Western countries.

“I can only confirm that Russia planned acts of air terror, not just against Poland but against airlines across the globe,” the prime minister, Donald Tusk, said during a meeting with Ukraine’s president, Volodymyr Zelensky.

Mr. Tusk did not elaborate, and it was unclear whether officials believed that Moscow was continuing to actively plan such an action.

Officials first became aware of the plot over the summer, when incendiary devices placed at shipping hubs in Britain and Germany ignited fires that caused minimal damage. In November, four Western officials briefed on intelligence about the operation said the fires had been part of a test of security measures carried out by Russia’s military intelligence service, known as the GRU.

The ultimate goal of the plot was not known, but intelligence agencies started an investigation into whether the intent was to destroy planes on American or European runways, or even blow up an aircraft midair.

By the fall, the White House became so concerned that President Biden ordered his national security adviser and the C.I.A. director to warn top aides of Russia’s president, Vladimir V. Putin, that such plotting could provoke a severe reaction from the United States. Any acts of sabotage that caused mass casualties would represent a serious escalation of conflict between Moscow and Washington, and the United States would hold Russia responsible for “enabling terrorism,” a senior official told The New York Times.

While the Kremlin has denied that its agents engage in sabotage, Western officials say Moscow has ordered its intelligence services to find ways to bring the war in Ukraine, soon to enter its fourth year, to Europe and the United States.

Many of the sabotage plots attributed to Russia appear amateurish, perhaps intended more to annoy than to terrorize. In December, Estonian authorities released details about a gang of GRU agents paid to break the windows of the interior minister’s car and deface World War II monuments, and in France Russian agents have been linked to antisemitic graffiti spray painted on walls.

But other episodes have been more sinister. Fires have broken out at arms factories supplying weapons to Ukraine as well as aboard buses and at shopping malls. And critical telecommunications cables crossing the Baltic Sea have been cut, though attributing these definitively to one country has been difficult. Last year, two assassins who were believed to have ties to Russia killed a Russian defector in southern Spain.

The sabotage campaign, officials said, is being waged almost exclusively by the GRU, an agency that has carried out sabotage and assassination operations in Europe since before Mr. Putin’s 2022 invasion of Ukraine. Most notably, it was operatives from the GRU who used a highly potent nerve agent in the attempted assassination of Sergei Skripal, a GRU turncoat who was living in Britain.

After Russia’s full-scale invasion of Ukraine, the GRU’s activities in Europe abated somewhat as European countries expelled operatives and limited travel for Russians. But in the past year, the agency has figured out ways to restore its operations. Officials say that many acts of sabotage are carried out by hired proxies, sometimes recruited over the internet. That is one reason the operations have so far achieved limited results. But officials worry that recruiting people over the internet to commit such operations also increases the risk of dangerous and potentially deadly mistakes.

“The GRU in particular is on a sustained mission to generate mayhem on British and European streets,” Ken McCallum, the director general of Britain’s Mi5, the country’s domestic intelligence service, warned in rare public remarks last fall. “We’ve seen arson, sabotage and more. Dangerous actions conducted with increasing recklessness.”

For President-elect Donald J. Trump, the Israeli-Gaza cease-fire deal was key for two reasons.

It removed one of the most vexing international conflicts that hovered over the start of his second term, and it gave Mr. Trump, who was known during his real-estate developer days in New York City as a “deals guy,” something to claim credit for as an early win — even if it happened before he took office.

In a posting on social media on Wednesday, Mr. Trump declared that the deal “only happened as a result of our Historic Victory in November.”

The contours of the deal were not especially different than what President Biden had sought in May. But multiple people with insight into the process said that Mr. Trump’s win in November, along with the involvement of members of his incoming administration, were key parts in moving things forward.

The aftermath of the deadly Oct. 7, 2023, attacks by Hamas had been a backdrop to the U.S. presidential race in 2024. As Mr. Trump emerged not just as the Republican nominee but the survivor of an assassination attempt in July, his relationship with Prime Minister Benjamin Netanyahu of Israel improved. (The ties had frayed after Mr. Netanyahu congratulated Mr. Biden on winning the 2020 election.)

Fear of what the often unpredictable Mr. Trump — who months ago said the world knows that he’s “crazy,” using an expletive for emphasis — might do on the world stage has become a key theme in private discussions among foreign leaders.

So the deal — forged with significant involvement by Mr. Trump’s Mideast envoy, Steve Witkoff — allowed Mr. Trump to begin his term with one less problem.