"I want to live in a free Russia, I want to build a free Russia," Navalnaya said in a video message released three days after her husband's death.
"Vladimir Putin killed my husband," Navalnaya added, vowing to work with supporters to "create a new Russia."
"By killing Alexei, Putin killed half of me - half of my heart and half of my soul," Navalnaya also said, as cited by the Reuters news agency. "But I still have the other half, and it tells me that I have no right to give up."
She declared: "I will continue the work of Alexei Navalny, continue to fight for our country."
Navalnaya urged fellow Russians to "stand next" to her, Reuters reported.
She said: "I ask you to share the rage with me. Rage, anger, hatred towards those who dared to kill our future."
Poland's president, prime minister and top diplomat have paid tribute to Navalny, who died in an Arctic penal colony last Friday, according to reports.
Russian authorities said Navalny died of natural causes.
Navalnaya said in her message: "We know why exactly Putin killed Alexei three days ago. We'll tell you about it soon. We will definitely find out who exactly and how exactly committed this crime. We will name names and show faces."
She continued: "But the main thing we can do for Alexey and for ourselves is to continue to fight. Bigger, more desperate, more furious than before. I know it seems like nothing more is possible. But we need more. Let's all gather together into one strong fist and hit this maddened regime, Putin, his friends, the bandits in uniform. For the thieves and murderers who crippled our country."
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Source: Reuters, IAR, PAP, rus.postimees.ee