but first to Russia, where top opposition figure Alexei Navalny is reported dead this evening.

AMNA NAWAZ: Russian authorities claimed he died early today at the remote Arctic prison where he was held, often in isolation.

The 47-year-old anti-corruption campaigner and politician had for years exposed the hidden fortunes of many top Russian officials, including President Vladimir Putin, incurring their wrath.

President Biden said the news of Navalny's death in Russia, where many opposition figures have been killed, did not surprise him, but it did outrage him.

He went from being Vladimir Putin's staunchest critic to leading Russia's strongest anti-corruption movement and eventually Russia's most prominent political prisoner.

ALEXEY NAVALNY, Russian Opposition Leader (through translator): I believe.

I am confident and declare that they are not the masters of our country and never will be, and a huge number of people agree with me.

AMNA NAWAZ: Russian prison authorities today announced Alexei Navalny died in a penal colony in the Arctic Circle, where he was serving a 19-year sentence on extremism charges widely seen as politically motivated.

In a statement, prison services said Navalny felt ill after a walk and -- quote -- "almost immediately losing consciousness."

He was last seen in yesterday's court hearing, alive but gaunt after three years in prison, and seemingly laughing and well.

His wife, Yulia Navalnaya, took the stage at Munich's security conference hours after he was reported dead.

YULIA NAVALNAYA, Wife of Alexei Navalny (through translator): We cannot believe Putin and Putin's government.

They always lie.

But if this is true, I want Putin and his entire entourage to know that they will bear responsibility for what they have done with our country, with my family, and with my husband.

And this day will come very soon.

AMNA NAWAZ: At the White House this afternoon, President Biden was unequivocal.

JOE BIDEN, President of the United States: Make no mistake.

Putin is responsible for Navalny's death.

Putin is responsible.

What has happened to Navalny is yet more proof of Putin's brutality.

AMNA NAWAZ: The son of a military officer, Alexei Navalny was born in the village of Butyn' outside of Moscow.

In the late 1990s, he earned a law degree from Moscow's Friendship of the People's University and grew into Russia's most well-known political opposition figure crusading against corruption.

He called Putin's United Russia Party -- quote - - "the party of crooks and thieves."

He led mass protests in 2011 and again in 2012, when it was clear President Putin would regain the presidency.

Our Margaret Warner interviewed Navalny then.

ALEXEI NAVALNY (through translator): This is not an election.

This procedure is aimed at only one thing, the appointment of Prime Minister Putin once again the president, seemingly for life.

AMNA NAWAZ: In 2013, he broke into politics with a mayoral run in Moscow.

And though he didn't win, he did beat the incumbent Putin-backed mayor.

House arrest followed in 2014 for embezzlement and later convictions on fraud and money laundering, charges Navalny denied.

Despite being barred from running in 2016, he announced he would run against Putin for the presidency in 2018.

More arrests and repression followed, a 2017 detention for an unsanctioned rally, one of the country's largest opposition demonstrations in years, 187 cities, tens of thousands of Russians, all protesting corruption.

Despite repeated threats, Navalny forged on with his anti-corruption foundation, investigating Russia's elite and bypassing state-run media with YouTube videos garnering millions of views.

ALEXEI NAVALNY (through translator): This is our country, and these swindlers are stealing our money.

Everyone should fight however he can.

AMNA NAWAZ: His fight nearly killed him once already.

In 2020, Navalny was in a coma for two weeks after being poisoned by a lethal nerve agent.

Russia denied poisoning him, but a recorded call to a Russian intelligence agent featured in this 2022 CNN documentary revealed the poison was planted in his underpants.

MAN (through translator): So, if they were in the air longer, things would have gone as planned.

AMNA NAWAZ: Despite being evacuated to Germany for treatment, Navalny made the decision to return to Russia in 2021.

He was jailed as soon as he landed in Moscow and has been behind bars ever since.

Today, hundreds gathered across European cities chanting anti-Putin slogans and blaming him for Navalny's death.

Even across Russia, where dissent is punished, residents mourned his death.

RADIK MIDULIN, Russia Resident (through translator): He's a Russian patriot.

He wanted the country to become better.

AMNA NAWAZ: Navalny himself saw this day coming.

ALEXEI NAVALNY: My message for the situation when I am killed is very simple: Don't give up.