Warsaw, Poland - US Vice President Kamala Harris called Russian opposition figurehead Yulia Navalnaya, the widow of late Kremlin critic Alexei Navalny, to discuss Thursday's massive Russia-West prisoner exchange, Navalnaya's spokeswoman said.

Harris called her "to discuss the exchange and express her support, noting Alexei and Yulia's contribution to the fight for a democratic Russia," the spokeswoman, Kira Yarmysh, said on X.

The swap included three former members of Navalny's regional campaign apparatus, as well as a former ally of Navalny, Ilya Yashin.

Navalnaya's team said earlier that Navalny, Russian President Vladimir Putin's top opponent, was due to have been included in a prisoner swap before his sudden death in a remote Russian prison colony in February.

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Navalnaya and Western countries have blamed his death on the Kremlin.

Yarmysh said Navalnaya thanked Harris in Thursday's call "for the US assistance in organizing the exchange."

She also "called on the international community to facilitate the release of other Russian political prisoners," Yarmysh said.

Harris is set to become the Democratic US presidential nominee after Joe Biden ended his re-election bid.

Like Biden, she has been a staunch backer of Ukraine since Russia launched its full-scale military offensive in February 2022.

Earlier this year, she said Navalny's death was "a further sign of Putin's brutality."

She has also called Russia's actions in Ukraine "horrendous atrocities," "gruesome," "barbaric," and "inhumane."

Kremlin spokesman Dmitry Peskov last month noted the "unfriendly rhetoric" against Russia used by Harris.