Bono honored late Russian dissident Alexei Navalny at a U2 show at the Las Vegas Sphere over the weekend.

The U2 front man, 63, led the crowd at Saturday's show of the band's residency in chanting Navalny's name following his mysterious death in a Siberian prison.

'Apparently Putin would never, ever say [Navalny's] name. So I thought tonight, the people who believe in freedom must say his name. Not just remember it, but say it,' an impassioned Bono told the crowd at the Sphere.

Before performing Crowded House's Don't Dream It's Over, Bono also voiced his support for the people of Ukraine and his opposition to Vladimir Putin. 

'Next week it'll be two years since Putin invaded and tried to destroy the hard-won freedoms [of the Ukrainian people] Bono said. 

'Next it'll be Poland, next it'll be Lithuania, East Germany... who knows where this man will or won't go. 

'To these people freedom is not just a word in a song. For these people freedom is the most important word in the world — so important that Ukrainians are fighting and dying for it. And it's so important that Alexei Navalny chose to give his up.'

Bono was referencing Navalny's decision to go back to Russia knowing he would be arrested and sent to Siberia upon landing over his fierce opposition to tyrant Putin.

The details of Navalny's death remain unclear as of Monday, with a Navalny spokesman saying his body will not be released for 14 days.

The news sparked shock and anger around the globe, with world leaders and commentators quickly pointing the finger at the Kremlin. 

Navalny was 'brutally murdered by the Kremlin,' Latvia's president declared, while Ukrainian president Volodymyr Zelensky said it was 'obvious' Putin had ordered the dissident's killing.

President Joe Biden, on his part, blamed Putin for Navalny's death, telling the press  he was both 'not surprised' and also 'outraged' to hear that the 47-year-old Russian opposition leader had died - and was looking into ways to respond.

As Putin's fiercest foe, Navalny crusaded against official corruption and staged massive anti-Kremlin protests - drawing the merciless retribution of the Kremlin. 

He once survived an assassination attempt involving the Novichok nerve agent, but returned to his homeland upon his recovery, despite knowing he would be arrested.

Ever since, he had been serving time on extremism charges after being sentenced to 19 years behind bars, and in December was moved from a prison in central Russia to a 'special regime' penal colony known as 'Polar Wolf' above the Arctic Circle.

He was last seen via video link during a court hearing on Thursday.

Dressed in black prison uniform, he appeared to be in good spirits - his trademark humor back on show.

'Your Honor, I will send you my personal account number so that you can use your huge salary as a federal judge to ''warm up'' my personal account, because I am running out of money,' he said.

Navalny's mother Lyudmila said she had seen her son in the prison colony on Monday. At the time, she said: 'He was alive, healthy, cheerful.'

But the Federal Prison Service said in a statement today that Navalny felt unwell after a walk and lost consciousness. An ambulance arrived to try to save him, to no avail.

Bellingcat journalist Christo Grozev - an ally of Navalany who has followed his trial closely, said: 'I have no doubt that the death of Alexei Navalny is not natural.

'Even propagandist Russian channels, linked to the special services, called this a political assassination. Who are we to doubt their own words?'