There's been international outrage and condemnation of the news that the most prominent opposition leader in Russia, Alexei Navalny, has died suddenly in prison, according to the country's prison service. The 47-year-old was President Putin's most prominent and outspoken critic and had been jailed on extremism charges which were widely considered to be politically motivated. President Biden said tonight that President Putin was responsible for Mr. Navalny's death, and it was yet more proof of his brutality. Alexei Navalny's wife, Yulia, said if the reports were true, Vladimir Putin would not go unpunished for her husband's death. Let's go first tonight to Moscow and to our Russia editor, Steve Rosenberg. Steve.

Rita, of all the critiques and opponents that Vladimir Putin has faced, Alex Zeyn, the Vailny, was by far the most active, the most vocal, and the most dangerous to the authorities. Why? Because he had charisma, he had organizational skills, and he had this rare ability to connect with people. But in recent years, his friends and family had feared for his safety, especially after he was put in prison three years ago. And today came the shock announcement that he was dead. Smiling, cracking jokes. This was Alexander Vailny yesterday, as he gave testimony by video link from prison. Even court officials managed to smile. But today, Russia's Prison Service said that Mr. Navalny was dead. It claimed that inside this penal colony, he'd fallen unconscious, and that medical teams couldn't save him. Russian TV rarely mentions Alexei Navalny. It read out the Prison Service statement about his death and moved on to other news. He was Vladimir Putin's most vocal critic. A protest leader, an anti-corruption campaigner who'd long clashed with the Kremlin. I remember this six years ago. Alexei Navalny is Russia's most prominent opposition figure and President Putin's most vocal critic. He's been barred I'm running in the presidential election.

He's now being arrested by police. In 2020, in Siberia, he'd been poisoned with a nerve agent and airlifted to Germany for life-saving treatment. He accused the Kremlin Vilenin of trying to assassinate him. But as a politician, he felt he couldn't stay away from Russia. When he returned the following year, he was arrested on arrival. He been in prison ever since, his friends and family fearing for his safety. Just hours after Alexander Vileny was reported dead, his wife, Yulia, made a dramatic appearance at the Munich Security Conference. She couldn't confirm his death, but... If it's true, I want Putin and his whole entourage, his friends and his government, to know that they will be held responsible for everything they've done to our country, to my family, and to my husband. And this day will come very soon. And once she'd finished speaking, from the hall, a standing ovation. And Back in Russia, President Putin was meeting industrial workers. He made no mention of Alexey Navalny. He knew that by taking on the authorities, he was taking a risk. My message for the situation when I'm killed is very simple, not give up. Not all Russians supported Alexey Navalny, but in Moscow and in other Russian towns, people came out to remember him.

In a country where dissent has been silenced, for many here, just doing this was an act of courage. So at this makeshift shrine, people have been putting down portraits of Alexey and the Vyhny. They've been laying roses and carnations and lighting candles, as you can see. And here at the end, there's a sign which says, We won't forget and we won't forgive. There's a palpable sense of disbelief. I was seeing the news on my phone, and first my reaction was like, It's just a joke. It can't real. But then the news was come and more and more and more, and I was crying for One hour. What was your reaction when you heard the news about his death? I was with my friends. I was broken. I really I thought that it couldn't happen. Never. That's the phrase I've heard so often from Russians in recent times. We never thought it could happen. Steve Rosenberg, BBC News, Moscow.

Well, there's been shock and dismay around the world at the news of Mr. Navalny's death. Our security correspondent, Gordon Carrera, has more.

Tonight, vigils have been marking the death of Alexei Navalny, like this one in Tablisi, Georgia. Others have taken place in London and in Berlin. He is the latest and most high profile of Vladimir Putin's critics to meet an untimely end. It's a moment which has been met with outrage from Western leaders.

Make no mistake. 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. Are you looking at increasing sanctions on Russia right now? We're looking at a whole number of options. That's all I'll say right now. We should be clear about what has happened here. Putin's Russia imprisoned him, trumped up charges against him, poisoned him, sent him to a Arctic penal colony, and now he's tragically died. We should hold Putin accountable for this, and no one should be in any doubt about the dreadful nature of Putin's regime in Russia.

The suspicions around Navalny's death are fueled by the fate of other Putin critiques. Last August, Evgeny Prigozhin died, the mercenary who'd led an armed mutiny in Russia. He was killed in a plane crash. It was, the Kremlin said, an accident. In 2015, leading opposition politician Boris Nemtsov was killed, shot on a bridge in the shadow of Red Square. Again, the Kremlin denied any role. It's not just inside Russia that opponents Vladimir Putin have been targeted. In 2018, Serge Skripal, who spied for Britain, was targeted in Saldsbury, along with his daughter. Novichok, the same nerve agent once used on Navalny, nearly killed them. In 2006, there was the death of Alexander Litvinenko, a former intelligence officer and a fierce critic of Vladimir Putin, poisoned with radioactive polonium in London. Since Vladimir Putin gave the order for the invasion of Ukraine two years ago, questions have grown about how far Russia's leader is willing to go. This is what Ukraine's President had to say today. Obviously, he was killed by Putin, like thousands of others who have been tormented and tortured because of this one person.

Putin does not care who dies as long as he retains his position, and that is why he must not keep anything. Putin must lose everything.

It's not yet clear exactly what happened to Alexei Navalny, but Vladimir Putin's critiques seem to know who they hold responsible. Gordon Carrera, BBC News.

Well, in a moment, we'll go back to Steve Rosenberg in Moscow. But first, let's talk to our Chief International Correspondent, Lise Douzet, who's at that security conference in Munich for us. And Lise, world leaders are openly pointing the finger at Vladimir Putin, but is that outrage likely to be turned into any action?

Well, three years ago, President Biden, vowed devastating consequences if Alexei Navalny was to die behind bars. I heard much the same today from Lord Cameron, wherein he said, Here in Munich, there should be consequences. But And what? So much of what could be done to punish or try to contain President Putin has already been done. Wide-ranging sanctions imposed after Russia's full-scale invasion of Ukraine two years ago. Although many question the effectiveness of the sanctions, President Putin has been indicted by the International Criminal Court, a court he mocks. But earlier today, I also spoke to Estonia's Prime Minister, Kaya Callas. And like all of Russia's immediate neighbors, she's always thinking about how to deal with this threat right on the borders. And she had two steps that she recommended Russia's foreign assets, seizing them and spending that money to rebuild Ukraine, something she says that President Putin feels, and secondly, establishing a special tribunal for accountability. For today and tomorrow, the world will wait for confirmation from Alexei Navalny's family, confirmation that the prison services account that he's is true, and that many around the world will then do everything to ensure that his courage and sacrifice were not in vain.

Steve, in Moscow, Alexi Navalny was the most prominent of Putin's critiques. Where does this now leave opposition to the President in Russia?

Well, even before today, these were very dark times for the Russian opposition. Where are the main Russian opposition leaders right now. They've either fled into exile or they're in prison in Russia. Alexander Vyhling himself, of course, was in prison. Now he's dead. Also, keep in mind that ever since the full-scale Russian invasion of Ukraine, the Russian authorities have passed a whole string of laws, new laws, repressive laws, aimed at silencing dissent, silencing criticism of the authorities of the Kremlin and of the war in Ukraine. But I tell you what struck me most today on what was a very dark day here in Russia, just chatting to some of those people who were laying flowers. I mean, despite their clear sense of shock, some of them said to me that despite everything, they still have hope that things could get better, that Russia does have a better future, ultimately. It was as if they were clinging to this hope, like some shaft of light in the dark.