Russian President Vladimir Putin did not see the video in which Alexei Navalny’s widow vowed to continue his fight against the Kremlin, his spokesman said, and dismissed her allegations that Mr Putin had killed the country’s opposition leader as “unfounded” and “insolent”.

In the video released on Monday, Yulia Navalnaya accused Mr Putin of killing her husband in the remote Artic prison and alleged that officials’ refusal to hand over his body to his mother was part of a cover-up.

“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, Ms Navalnaya said.

She suggested her husband might have been killed with a Novichok-style nerve agent.

Russian authorities said that the cause of Mr Navalny’s death Friday is still unknown and the results of any investigation are likely to be questioned abroad.

Many Western leaders have already said they hold Mr Putin responsible for the death.

“These are absolutely unfounded, insolent accusations about the head of the Russian state,” Kremlin spokesman Dmitry Peskov said.

Mr 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 Mr 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 Mr Putin’s unrelenting crackdown on the opposition.

Mr Navalny, 47, 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.

Josep Borrell, the European Union’s foreign policy chief, called for an international investigation into Mr Navalny’s death but Mr Peskov said the Kremlin would not accept any such demand.

Since Mr Navalny’s death, around 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.

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

Mr Peskov said on Tuesday that police were acting “in accordance with the law” when they detained people paying tribute to Mr Navalny.

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

After the last verdict that handed him a 19-year term, Mr 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, Ms 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 said.