Russian opposition leader Alexei Navalny was poisoned before his unexpected death last year in an Arctic penal colony, according to a video his widow, Yulia Navalnaya, posted on X.

Navalny was 47 years old when he died in Feb. 2024. Russia’s prison service reported he was found unresponsive after feeling unwell following a walk around the high-security facility in a remote town above the Arctic Circle, where he was serving a combined 30 ½-year jail sentence.

His widow has repeatedly accused the Kremlin and Russian President Vladimir Putin of being involved in Navalny's death. Russian officials have said only that Navalny died of natural causes and have vehemently denied involvement.

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She had also accused the prison service of withholding his remains from his family. Eventually, his remains were given to his mother about a week after his death.

"The killers worked carefully to erase traces. But we have managed to preserve some evidence,” Navalnaya said on X early Wednesday, adding that they were able to "securely smuggle" some of Navalny's biological material to laboratories abroad.

"These labs, in two different countries, reached the same conclusion. Alexei was killed. More specifically, he was poisoned," said Navalnya. She continued to blame Putin for Navalny's "murder."

Navalnaya did not give any further details on the tests or which countries were involved.

"I demand that the laboratories that conducted the analyses publish their results," she added. "Stop pandering to Putin on account of so-called higher considerations. While you remain silent, he doesn't stop."

Last year, U.S. officials said they did not believe Putin was ultimately responsible for the death of Navalny.