MOSCOW -- Russian opposition politician Alexei Navalny was close to being freed in a prisoner swap at the time of his death, Maria Pevchikh, a Navalny ally, said on Monday, repeating her allegation that President Vladimir Putin had him killed.

Speaking on YouTube, Pevchikh said talks about exchanging Navalny and two unnamed U.S. nationals for Vadim Krasikov, a Russian FSB security service hit man in jail in Germany, were in their final stages at the time of his death.

Navalny, 47, died at an Arctic penal colony on Feb. 16. The Kremlin has denied Russia had any involvement in his death. Navalny's death certificate stated that he died of natural causes, according to his supporters.

Pevchikh did not name the two U.S. nationals in contention to be swapped along with Navalny. But the United States has said it is trying to return Evan Gershkovich, a reporter for the Wall Street Journal and Paul Whelan, a former U.S. marine.

"Alexei Navalny could be sitting in this seat right now, right today. That's not a figure of speech, it could and should have happened," said Pevchikh.

"Navalny should have been out in the next few days because we got a decision about his exchange. In early February, Putin was offered to exchange the killer, FSB officer Vadim Krasikov, who's serving time for a murder in Berlin, for two American citizens and Alexei Navalny."

Pevchikh said she had confirmation that negotiations for the swap were in their final stages on the evening of Feb. 15.

Navalny, she alleged, had been killed a day later because Putin could not tolerate the thought of him being free.

Pevchikh said Navalny's allies had been working since the start of the Ukraine war on a plan to get him out of Russia as part of a prisoner exchange involving "Russian spies in exchange for political prisoners."

She said they had made desperate efforts and tried to find intermediaries, even approaching the late Henry Kissinger, but said Western governments had failed to show the necessary political will.

"Officials, American and German, nodded their heads in understanding. They recounted how important it was to help Navalny and political prisoners, they shook hands, made promises and did nothing."

(Reporting by Filip Lebedev and Andrew Osborn;Editing by Mark Trevelyan)