Russia - Alexei Navalny's widow said Monday that Russia's President Vladimir Putin killed her husband, as she vowed to carry on his work, three days after he died in an Arctic prison.

Holding back tears in a video address published Monday, Yulia Navalnaya said: "Three days ago, Vladimir Putin killed my husband, Alexei Navalny."

Prison authorities said Navalny died after losing consciousness following a walk in his prison colony in Kharp, 2,000 miles northeast of Moscow inside the Arctic circle.

"Alexei died in a prison colony after three years of torment and torture," Navalnaya said Monday.

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Navalnaya, who was by her husband's side for more than a decade as he became a vocal critic of Putin, vowed to continue his work.

"The most important thing we can do for Alexei and for ourselves is to keep fighting, more desperately and more fiercely than before," she said.

"We need to seize every opportunity to fight against war, against corruption, against injustice, to fight for fair elections and the freedom of speech, to fight to take back our country."

She also vowed to uncover the people who she said had killed her husband.

"We know exactly why Putin killed Alexei three days ago... We will definitely find out exactly who carried out this crime and how it was carried out. We will name names and show faces," she said.

The Kremlin said earlier on Monday that an investigation into Navalny's death was ongoing and slammed Western governments that have said Putin carries responsibility for his death.

Russian authorities have so far refused to hand over Navalny's body to his mother and lawyer, enraging his supports who have said it was a move by the "killers" to "cover their tracks."

Russian officials had accused Navalny of working for the CIA, while Amnesty International stripped him of his "prisoner of conscience" status over past racist and xenophobic statements he did not renounce.