Navalny, 47, died at an Arctic penal colony on Feb. 16. The Kremlin, which casts Navalny and his supporters as U.S.-backed extremists, has denied state involvement in his death. Navalny's death certificate said he died of natural causes, according to supporters.

There was no immediate comment from the Kremlin and Navalny ally Maria Pevchikh, who is based outside Russia, did not present documentary evidence for her assertion.

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.

"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, who chairs the board of Navalny's anti-corruption foundation.

"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."

Krasikov was jailed for life in Germany after being convicted of killing an exiled Chechen-Georgian dissident in Berlin in 2019. Putin signalled in an interview with U.S. journalist Tucker Carlson this month that he wanted to get Krasikov, whom he cast as a patriot, back.

A German government spokesperson declined to comment on Monday.

Pevchikh, who has been designated a "foreign agent" by Russia where the authorities accuse her of involvement in an extremist organisation, said she had received 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. She did not explain why Putin had not simply refused to swap Navalny if he was opposed to such an exchange.

She said that businessman Roman Abramovich had been the one to float the idea to Putin of exchanging Navalny. There was no immediate comment from Abramovich.

Pevchikh did not name the two U.S. nationals purportedly 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.

Russia accuses both men of espionage, something they deny.

'NAVALNY AGREED'

A Russian source with knowledge of the discussions told Reuters separately that the prisoner exchange had been meant to take place in the middle of February and that both Navalny and his wife had agreed to it.

The source also said Abramovich had been involved in the talks.

"Initially, the plan envisaged an exchange only involving Gershkovich, and Abramovich had discussed it with Putin. The only person Putin was ready to swap him for was Krasikov. But the Germans were categorically against it, because it was an American problem. When Navalny appeared within this plan, the Germans finally agreed," the source said.

"Everything was finally confirmed when (German Chancellor Olaf) Scholz went to the States (he held White House talks on Feb. 9). The details of when and where all this would happen were already being discussed."

Putin, who has yet to comment on Navalny's death, said this month that talks between Russian and U.S. intelligence agencies were going on related to Gershkovich, but made no mention of Navalny, whose name he does not usually mention publicly.

Speaking earlier on Monday, the Kremlin had called allegations that Russian authorities had pressured the mother of Navalny to try to get her to agree to a private funeral absurd, saying Putin had not been involved in decisions on Navalny's body.

"The Kremlin has nothing to do with this, so the Kremlin cannot exert pressure. This is another absurd statement by these (Navalny) supporters," Kremlin spokesman Dmitry Peskov said.

The late opposition politician's body was handed over to his mother in the Arctic city of Salekhard on Saturday.

The arrangements for his burial, expected to take place in Moscow, have yet to be announced. Navalny's spokeswoman said on Monday that his team was looking for a venue where a public farewell ceremony could take place by the end of this week.