It is “likely” Russian opposition leader Alexei Navalny was killed ahead of the country’s election next month to “crush” dissent, a Russia expert has said.

The UK has joined other western countries in condemning the Kremlin after Russia’s federal prison service said in a statement that the 47-year-old politician and anti-corruption campaigner had died.

According to the agency, he became unwell after a walk on Friday and lost consciousness.

An ambulance arrived but he died despite attempts to resuscitate him, it said.

Experts from King’s College London said Mr Navalny, who was one of the most outspoken critics of Russian President Vladimir Putin, symbolised hope and democratic change for many Russians.

Dr Maxim Alyukov, research fellow at the university’s Russia Institute, described Mr Navalny’s death as a “political killing”.

He added: “It is likely that he has been killed ahead of the March election, to demotivate and crush any potential dissent.

“Given Putin’s recording of physically eliminating opponents, it would not be a surprise at all.

“Elections, even if tightly controlled, still can serve as focal points for discontent, and there have been alternative candidates successfully campaigning for registration demonstrating that there is a demand of peace and change of power.

“Given Navalny’s significance and the fact that many associated democratic change in Russia with him, his death will be a signal that will shock and demotivate many, demonstrating that resistance is futile.

“He has been consistently tortured and denied medical treatment.

“Navalny was active in communicating with the public from prison via his lawyers, and his statements were giving hope to many dissidents both inside and outside Russia.”

Professor Gulnaz Sharafutdinova, professor of Russian politics and director of the university’s Russia Institute, said Mr Navalny’s death could lead to protests on the streets of Russia.

She added: “The Kremlin tried to get rid of Navalny using different means. His death (if confirmed) will be heartbreaking for many thousands of Russians who believe and fight for different Russia.

“His role as a model of a politician who sacrificed his life for his beliefs and principles will stay on and inspire others.

“But this moment is a moment for grief. We will see how the grieving will unfold in Russia in the next few days probably.

“This news could interfere with the presidential elections in Russia. But that would depend on people’s actions on the ground.”

Dr Marc Berenson, senior lecturer at the university’s School of Politics and Economics said: “Navalny’s death, perhaps, constitutes the most prolonged murder in Russian history.

“Having survived multiple attempts on his life over the years, the conditions and treatment that Navalny endured while imprisoned by the Kremlin since his return to Russia in 2021 surely would have alone caused a slow death, absent any immediate deliberate actions.

“The manner in which the Kremlin has treated its own citizens, including its own soldiers on the front lines in Ukraine, should be yet another wake up call for the West, and particularly the US Congress, as to just how dangerous an enemy Russia has become.”

Mr Navalny, who campaigned against official corruption and organised major anti-government protests, has been behind bars since January 2021.

He was arrested on his return from Germany, where he had been recuperating after a nerve agent poisoning that he blamed on the Kremlin, on charges he dismissed as part of a politically motivated vendetta.

Since the start of his imprisonment, the opposition leader had remained a thorn in the side of Mr Putin via scathing attacks that his associates continued to post on social media.

Mr Navalny had been moved in December from his former prison in the Vladimir region of central Russia to a “special regime” penal colony, the highest security level of prisons in Russia, above the Arctic Circle.

His allies decried the transfer to the town of Kharp, in the remote Yamalo-Nenets region notorious for its long and severe winters, as yet another attempt to silence him.