TALLINN, Estonia — World leaders and Russian opposition activists wasted no time Friday in blaming the reported death of imprisoned opposition leader Alexei Navalny on President Putin and his government.

“It is obvious that he was killed by Putin,” President Zelensky, who was visiting Germany for the Munich Security Conference as he sought aid for his country as it fights off an invasion by Russia, said.

“Putin doesn’t care who dies — only for him to hold his position. This is why he must hold onto nothing. Putin must lose everything and be held responsible for his deeds,” Mr. Zelensky added.

Chancellor Scholz, whose country temporarily took in Navalny in 2020 after he was poisoned with a nerve agent, praised the Kremlin critic’s bravery and said his death makes clear “what kind of regime this is.”

“He has probably now paid for this courage with his life,” Mr. Scholz said, standing next to Mr. Zelensky. The German leader said he met Navalny at Berlin during his convalescence.

Navalny, 47, was serving a 19-year prison sentence on extremism charges at a remote penal colony above the Arctic Circle at the time of his death. He had been behind bars since he returned from Germany in January 2021, serving time on various charges that he rejected as a politically motivated effort to keep him imprisoned for life.

Navalny was “brutally murdered by the Kremlin,” tweeted Latvia’s president, Edgars Rinkēvičs. “That’s a fact and that is something one should know about the true nature of Russia’s current regime.”

Navalny’s associates stressed they didn’t have independent confirmation of his death in the reports that came from Russia’s penitentiary officials. His close ally Ivan Zhdanov said authorities “must notify the relatives” within 24 hours, but there hasn’t been any notification.

Navalny’s wife, Yulia Navalnaya, appearing at the Munich conference, said she did not know whether or not to believe it because “we cannot trust Putin and the Putin government. They always lie.”

“But if this is true, I want Putin and everyone around Putin, Putin’s friends, his government, to know that they will bear responsibility for what they did to our country, to my family and to my husband. And this day will come very soon,” she said.

The outpouring of sympathy for Navalny’s family and outrage at the Kremlin, which in recent years mounted an unprecedented crackdown on dissent, came from all over the world.

“If this is true, then no matter the formal cause the responsibility for the premature death is Vladimir Putin personally, who first gave the green light to the poisoning of Alexei and then put him in prison,” an exiled Russia tycoon turned opposition figure in exile, Mikhail Khodorkovsky, said in an online statement.

Other Russian opposition activists echoed him.

“If it is confirmed, the death of Alexei is a murder. Organized by Putin,” opposition politician Dmitry Gudkov said on social media. “Even if Alexei died of ‘natural’ causes, those were triggered by his poisoning and further torture in prison.”

Former world chess champion-turned-Kremlin opponent Garry Kasparov said “Putin tried and failed to murder Navalny quickly and secretly with poison, and now he has murdered him slowly and publicly in prison.”

“He was killed for exposing Putin and his mafia as the crooks and thieves they are,” tweeted Mr. Kasparov, who lives abroad.

The EU Commission president, Ursula von der Leyen, said Navalny’s death showed that “Putin fears nothing more than dissent from his own people.”

She called it “a grim reminder of what Putin and his regime are all about,” and added it should provide impetus to “unite in our fight to safeguard the freedom and safety of those who dare to stand up against autocracy.”

NATO’s cecretary-general, Jens Stoltenberg, said Russia has questions to answer.

“What we have seen is that Russia has become a more and more authoritarian power, that they have used repression against the opposition for many years,” Mr. Stoltenberg said.

Navalny, he said, “was in jail, a prisoner, and that makes it extremely important that Russia now answer all the questions that it will be asked about the cause of death.”

Vice President Harris, also at Munich, called his death, if confirmed, “a further sign of Putin’s brutality” and that “whatever story they tell — let us be clear — Russia is responsible.”

The British foreign secretary, David Cameron, echoed her remarks, saying “Putin’s Russia imprisoned him, trumped up charges against him, poisoned him, sent him to an Arctic penal colony and now he has tragically died. And we should hold Putin accountable for this.”

Russian lawmakers and other officials bristled at the Western outrage.  The head of a pro-Kremlin party, Sergei Mironov, said Navalny’s death helps Russia’s foes.

“Of course, health issues could have been the cause of death. But in any case a premature death of a notorious ‘opposition figure’, especially a month before the presidential election, is beneficial first and foremost to Russia’s enemies,” Mr. Mironov said in an online statement. “They will use it to the maximum to pressure us from the outside.”

A Russian foreign ministry spokeswoman, Maria Zakharova, said “the immediate reaction of NATO leaders to Navalny’s death in the form of direct accusations against Russia is self-exposing.” The death was still being investigated, but “the West’s conclusions are already ready,” she said.

Russian opposition activists in Europe called for rallies Friday at Russian embassies, and vigils were planned in Georgia, Israel and Armenia, according to the founder of Kovcheg, a group that helps exiled Russians, Anastasia Burakova.