Alexei Navalny’s widow has pledged to continue her dead husband’s fight for a free Russia and called on supporters to battle President Vladimir Putin with greater fury than ever.

Yulia Navalnaya released a bold video, accusing the Russian president of murdering her husband whose death in prison has been couched by authorities as “sudden death syndrome”.

Navalnaya also said “we know exactly why” Putin killed the Russian opposition leader and “will share this with you soon”.

She vowed to “find out who exactly carried out this crime and how exactly. We will name the names and show the faces”.

It comes as Navalny’s mother and lawyers have been blocked from the morgue and were told his body would not be released for 14 days.

Navalnaya accused Russian authorities of hiding Navalny’s corpse and of waiting for traces of the Novichok nerve agent to disappear from his body.

“Vladimir Putin killed my husband,” Navalnaya said.

“By killing Alexei, Putin killed half of me – half of my heart and half of my soul.

“But I still have the other half, and it tells me that I have no right to give up. I will continue the work of Alexei Navalny, continue to fight for our country.”

Navalny’s death robs Russia’s disparate opposition of its most charismatic and courageous leader as Putin prepares for an election that will keep him in power until at least 2030.

In her nine-minute message laced with rage, Navalnaya said she would continue the fight for a free and prosperous Russia so Navalny’s “unthinkable sacrifice” was not in vain.

“Fight and don’t give up. I am not afraid. Don’t you be afraid,” she said.

She urged those who wanted a free and happy Russia to “stand next to me”.

“I ask you to share the rage with me. Rage, anger, hatred towards those who dared to kill our future.”

An “outraged” European Union released a statement calling for an international investigation into Navalny’s death.

“The EU will spare no efforts to hold Russia’s political leadership and authorities to account, in close coordination with our partners; and impose further costs for their actions, including through sanctions.”

Navalnaya laid the blame for her husband’s death at the hands of Putin. Photo: X/Anton Gerashchenko

The Kremlin has denied involvement in Navalny’s death and says Western claims that Putin was responsible are “obnoxious and unacceptable”.

Putin has made no public comment, but has warned of a strong response if foreign powers try to meddle in Russia’s election.

Navalny, 47, fell unconscious and died suddenly on Friday after a walk at the “Polar Wolf” penal colony in the Arctic where he was serving a three-decade sentence, the prison service said on Friday.

The West and Navalny’s supporters have dismissed the service’s statement about his death, which has further deepened the schism between Moscow and the West caused by the Ukraine war.

The Kremlin said on Monday the investigation into his death was ongoing, while Russian investigators told Navalny’s mother and lawyers his cause of death was yet to be determined.

Navalnaya, 47, always supported her husband in his battles with the Russian authorities, attending his many court appearances, standing beside him at rallies and waiting for release from many prison terms.

“The main thing that we can do for Alexei and for ourselves is to keep fighting. More, more desperate, fiercer than before,” she said in her video message.

Navalny rose to prominence more than a decade ago by documenting and poking fun at what he said was the vast corruption and opulence of the “crooks and thieves” running Putin’s Russia.

He had been incarcerated at the IK-3 penal colony north of the Arctic Circle located in Kharp in the Yamalо-Nenets region about 1900km northeast of Moscow.

His death came just as Russian forces made their biggest advance in the Ukraine war since May 2023 and as the West debates how much more support to give to Kyiv.

US President Joe Biden blamed Putin for Navalny’s death and warned there could be consequences.

However, it is unclear what more the West can do after imposing on Russia what it says are already the toughest sanctions ever imposed on a major economy over the Ukraine war.

-with AAP