The widow of Russian Opposition leader Alexei Navalny vowed on Monday to continue his fight against the Kremlin while authorities denied his mother access to a morgue where his body is believed to be held after his death last week at an Arctic penal colony.

Fighting back tears, Yulia Navalnaya accused Russian President Vladimir Putin of killing her husband in a remote prison and vowed to punish him and other alleged perpetrators.

She also slammed the authorities, saying they were refusing to hand over the body to Navalny's mother to cover-up his alleged killing, and referred to his alleged earlier poisoning with a Soviet-era Novichok nerve agent.

Russian authorities said that the cause for Navalny's death Friday at age 47 is still unknown. He had been jailed since January 2021, when he returned to Moscow after recuperating in Germany from poisoning with a Novichok-type nerve agent that he blamed on the Kremlin. He received three prison terms since his arrest, on a number of charges he has rejected as politically motivated.

“They are cowardly and meanly hiding his body, refusing to give it to his mother and lying miserably while waiting for the trace of another Putin's Novichok to disappear,” Navalnaya said.

She urged Russians to rally behind her “to share not only the grief and endless pain that has enveloped and gripped us but also my rage."

“Rage, anger, hatred for those who dared to kill our future,” she said. “I address you with the words of Alexey, in which I really believe: It's not a shame to do little, it's a shame to do nothing. It's a shame to let yourself be intimidated.”

Navalnaya urged all those who mourn Navalny to unite to fulfill his dream of a “beautiful Russia of the future” so that “the unimaginable sacrifice” he made would not have been in vain.

“The main thing that we can do for Alexei and ourselves is to keep fighting,” she said. “Stronger, more fiercely and valiantly than we did before. We all need to get together in one strong fist and strike that mad regime, Putin, his cronies, bandits in epaulets, thieves and killers who mutilated our country.”

Navalny's spokesperson Kira Yarmysh said that the Investigative Committee, the country's top criminal investigation agency, informed Lyudmila Navalnaya that the cause of her son's death remained unknown and that the official probe had been extended. “They lie, buy time for themselves and do not even hide it,” Yarmysh posted on X, formerly Twitter.

Many world leaders blamed President Vladimir Putin and his government for Navalny's death. On Monday, EU foreign policy chief Josep Borrell said the bloc was mulling sanctions against Russia.

He noted the responsibility for Navalny's death lies with “Putin himself, but we can go down to the institutional structure of the penitentiary system in Russia”, to track down those involved and impose asset freezes and travel bans.