The widow of Aleksei A. Navalny said on Monday that she would carry on her husband’s work to bring about a democratic and free Russia, presenting herself for the first time as a political force and calling on his followers to rally alongside her.
Mr. Navalny’s sudden death in prison, which was announced by the Russian authorities on Friday, left a vacuum in Russia’s opposition. His supporters had wondered whether his wife, Yulia Navalnaya — who long shunned the spotlight — might step in to fill the void.
In a video released on Monday, Ms. Navalnaya, 47, signaled that she would. She said she was appearing on her late husband’s YouTube channel for the first time to tell his followers that the most important thing that they could do to honor his legacy was “to fight more desperately and furiously than before.”
“I am going to continue the work of Aleksei Navalny and continue to fight for our country,” Ms. Navalnaya said. “I call on you to stand beside me, to share not only in the grief and endless pain that has enveloped us and won’t let go. I ask you to share my rage — to share my rage, anger and hatred of those who have dared to kill our future.”
The nearly nine-minute video was crafted as an introduction of sorts to a new leader of the pro-democracy movement against President Vladimir V. Putin. It comes at a time when those opposed to the Kremlin strongman, who have sought to unite, feel more dispirited than ever.
Ms. Navalnaya had often pushed back against suggestions that she enter politics, telling Germany’s Der Spiegel magazine last year that “I don’t think this is an idea I want to play with.”
On Monday, she presented a different face in trying to rally her husband’s followers.
“I know it feels impossible to do any more, but we have to — to come together in one strong fist and strike with it at this maddened regime, at Putin, at his friends and his bandits in uniform, at these thieves and killers who have crippled our country,” she said.
The cause of Mr. Navalny’s death has not been established, and its circumstances have raised suspicions. President Biden blamed Mr. Putin personally, saying, “Make no mistake: Putin is responsible for Navalny’s death.”
Ms. Navalnaya echoed that sentiment, which is shared by many of her husband’s supporters, on Monday in her video.
“In killing Aleksei, Putin killed half of me, half of my heart and half of my soul,” Ms. Navalnaya, Mr. Navalny’s widow, said. “But I have another half left and it is telling me I have no right to give up.”
Her rousing message came as Mr. Navalny’s aides said that the opposition leader’s mother remained blocked from seeing her son’s body. Mr. Navalny’s spokeswoman, Kira Yarmysh, said the authorities had told his mother that the investigation into his death “has been extended” for an uncertain amount of time — and blocked her from seeing her son’s body.
“One of the lawyers was literally pushed out” from the morgue in the Arctic where Mr. Navalny’s body is believed to be, Ms. Yarmysh said in a post on the social media platform X. She added in another post, “They lie, buy time for themselves and do not even hide it.”
Russian investigators initiated an inquiry into the causes of Mr. Navalny’s death shortly after it was reported, a procedural move that allows them to hold the body for longer than normal.
Ivan Zhdanov, the head of Mr. Navalny’s anti-corruption Foundation, said that the delay meant that Russian officials were “cleaning up traces of their crime.”
“They are waiting for the wave of hatred and rage toward them to calm down,” Mr. Zhdanov said in a post on Telegram, the messaging app.
The Kremlin spokesman, Dmitri S. Peskov, rejected any suggestion of impropriety on Monday, saying that the investigation into Mr. Navalny’s death has been continuing “in accordance with the Russian law.”
More than 50,000 people have signed a petition to Russian investigators demanding the release of Mr. Navalny’s body, a campaign initiated by a Russia-based human rights group, OVD-Info.
Mourners have brought flowers to makeshift memorials across Russia, paying tribute to Mr. Navalny with an act of grief that has also served as a form of protest in a country where even the mildest dissent can risk detention.
The Russian authorities have tried to tamp down the scale of public mourning over Mr. Navalny’s death. Flowers have been quickly removed from memorials and the police have detained hundreds of people.
Anton Troianovski contributed reporting.