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 in an Arctic penal colony.

With her voice cracking at times in a video posted on social media, Yulia Navalnaya accused Russian President Vladimir Putin of killing her husband in the remote prison and alleged that officials' refusal to hand over the body to her mother-in-law was part of a cover-up.

Russian authorities said that the cause of Navalny’s death Friday at age 47 is still unknown — and the results of any investigation are likely to be questioned abroad. Many Western leaders have already said they hold Putin responsible for the death.

Navalny’s death has deprived the Russian opposition of its most well-known and inspiring politician less than a month before an election that is all but certain to give Putin another six years in power . It dealt a devastating blow to many Russians, who had seen Navalny as a rare hope for political change amid Putin's unrelenting crackdown on the opposition .

Navalny had been imprisoned since January 2021 , when he returned to Moscow after recuperating in Germany from a nerve agent poisoning 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" poison to disappear, Navalnaya said, suggesting her husband might have been killed with a Novichok-style nerve agent.

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."

She continued: “The main thing that we can do for Alexei and ourselves is to keep fighting. ... We all need to get together in one strong fist and strike that mad regime.”

On Monday, Ivan Zhdanov, the director of Navalny’s Anti-Corruption Foundation, said Navalny’s body would not be given to his mother for 14 days while a chemical examination of it takes place, according to a Russian investigator.

Navalny spokesperson Kira Yarmysh said the Investigative Committee, the country’s top criminal investigation agency, informed Lyudmila Navalnaya that the official probe into the death had been extended. “They lie, buy time for themselves and do not even hide it,” Yarmysh posted on X, the platform formerly known as Twitter.

With authorities offering no more information on the death after the brief initial statement, many Russians speculated about what might have happened to Navalny. Independent Russian outlets released reports attempting to shed light on his death. Some called into question the official narrative — but their reports were not possible to verify.

In Brussels on Monday, Navalny’s widow met with European Union foreign ministers and other officials. EU foreign policy chief Josep Borrell said the bloc was mulling sanctions against Russia and he also called for an independent international investigation into the causes of Navalny’s death.

He said 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 impose asset freezes and travel bans.

President Joe Biden said Monday his administration is also considering imposing additional sanctions on Russia.

Polish Foreign Minister Radek Sikorski described Navalnaya as “very dignified, very composed,” and urged his EU counterparts to act on Navalnaya’s request that the bloc impose sanctions on more of Putin's backers, beyond the oligarchs and other senior Russian officials already being targeted.

Kremlin spokesman Dmitry Peskov slammed the accusations from Western leaders as “boorish” and “inadmissible.”

“Those statements can’t do any harm to the head of our state, but they certainly aren’t becoming for those who make them,” Peskov said in a call with reporters.

Yarmysh said that Navalny’s 69-year-old mother and his lawyers were not allowed into the morgue in Salekhard, the capital of the Arctic Yamalo-Nenets region, on Monday morning. The staff didn’t answer when they asked if the body was there, Yarmysh said.

Asked when Navalny’s body could be handed over to his family, Peskov responded that the Kremlin was not involved in those proceedings, adding that the official probe was continuing in line with the law.

Observers said that the law allows authorities to keep the body for a long time if the investigation is ongoing and block any requests for an independent forensic study.

Navalny’s ally Ivan Zhdanov denounced the Russian authorities as “lackeys and liars.”

“It’s clear what they are doing now — covering up the traces of their crime,” he wrote Monday.

Since Navalny's death, nearly 400 people have been detained by police in Russia as they streamed to ad-hoc memorials and monuments to victims of political repression with flowers and candles to pay tribute to Navalny, according to OVD-Info, a group that monitors political arrests. The U.S. and British ambassadors also mourned Navalny's death at a memorial in Moscow.

Authorities cordoned off some of the memorials across the country and were removing flowers at night, but they kept appearing.

Over 50,000 people have submitted requests to the Russian government asking for Navalny's remains to be handed over to his relatives, OVD-Info said.

Russia’s Federal Penitentiary Service reported that Navalny felt sick after a walk Friday and became unconscious at the penal colony where he was being held. An ambulance arrived, but he couldn’t be revived, the service said.

After the last verdict that handed him a 19-year term, Navalny said he understood he was “serving a life sentence, which is measured by the length of my life or the length of life of this regime.”

In her video statement, 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,” she declared.