"You're not allowed to give up." That was the central message Russian opposition leader Alexey Navalny wanted to stress to his supporters in the event of his death. He said it in an Oscar-winning 2022 documentary about his life by Canadian director Daniel Roher, in which Navalny spoke about his political ideals and surviving a purported poisoning attack. 

"If they decide to kill me, it means that we are incredibly strong," said the anti-corruption campaigner who arguably turned into President Vladimir Putin's most potent political challenger. "We need to utilize this power to not give up, to remember we are a huge power that is being oppressed by these bad dudes."

Russian prison authorities said Friday that Navalny had died after going for a walk, feeling suddenly unwell and then collapsing. The Office of the Federal Penitentiary Service of Russia for the Yamalo-Nenets Autonomous District said medics at the IK-3 penal colony in Russia's far north were unable to revive him.

• Navalny appears healthy in court video day before reported death

Navalny's own team said they couldn't verify the information about his death on Friday, but the following day they confirmed it, saying he was "murdered." U.S. Vice President Kamala Harris unequivocally placed the blame on Putin's government.

"This is of course terrible news, which we are working to confirm," Harris said at the Munich Security Conference in Germany. "My prayers are with his family, including his wife Yulia, who is with us today, and, if confirmed, this would be a further sign of Putin's brutality. Whatever story they tell, let us be clear: Russia is responsible."

Yulia Navalnaya, Navalny's wife, spoke on stage at the Munich conference after Harris.

"You've probably all already seen the terrible news coming today. I thought for a long time whether I should come out here or fly straight to my children. But then I thought, 'What would Alexey do in my place?' And I'm sure he would be here. He would be on this stage."

She made it clear that she didn't trust any information coming from Russian government officials.

"They always lie. But if this is true, I want Putin, everyone around him, 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," Navalnaya said. "I want to call on the entire world community, everyone in this room, people all over the world, to unite together and defeat this evil, to defeat the terrifying regime that is now in Russia."

Russia has been condemned globally for its invasion of neighboring Ukraine, which sparked a grueling war set to enter its third year on Feb. 24. Navalny was a fierce critic of what he called the "stupid war" launched by "madman" Putin.

In a cruel twist, Putin and his political allies — who have run Russia for decades — have used the war as a pretext to enact harsh new laws in the name of national security, dramatically curbing free speech. Laws put on the books over the last several years have given the government power to lock up anyone who criticizes Russia's military or its actions in Ukraine.

It's all part of a wider crackdown on dissent that reached a crescendo after pro-Navalny protests swept across the nation following the opposition leader's 2021 arrest, and then took on new dimensions amid the Ukraine war.

Hundreds of politicians, opposition activists, journalists and civil society figures — including some of Navalny's own top aides — are in prison or have fled Russia into exile.

Street protests in Russia are illegal without prior permission, which officials don't grant to anyone known to oppose the government.

In:
• Democracy
• Prison
• Alexei Navalny
• Alexey Navalny
• Russia
• Vladimir Putin
• Free Speech

Tucker Reals

Tucker Reals is cbsnews.com's foreign editor, based in the CBS News London bureau. He has worked for CBS News since 2006, prior to which he worked for The Associated Press in Washington D.C. and London.