Russia has expressed "indignation" at comments by Pope Francis singling out the alleged role of Russian ethnic minorities in Moscow's military intervention in Ukraine, news agencies reported Tuesday.

Pope Francis in an interview published Monday said that some of the "cruelest" actors among Russia's ranks in Ukraine "are not of the Russian tradition," but minorities like "the Chechens, the Buryati and so on."

Russia's state-run RIA Novosti news agency reported Tuesday that Moscow's ambassador to the Vatican had lodged an official complaint in response.

"I expressed indignation at such insinuations and noted that nothing can shake the cohesion and unity of the multinational Russian people," Russian ambassador to the Vatican Alexander Avdeev told the agency.

Moscow was accused in September of drawing disproportionately from ethnic minorities in Siberia and in its Caucasus region when the Kremlin announced a draft of hundreds of thousands of men to the military.

Kremlin critics say minorities from impoverished and isolated regions are dying are in larger numbers in Ukraine compared to ethnic Russians.

But they have also been accused in Ukraine of playing outsized roles in places like Bucha, where the Russian military allegedly killed civilians.

Foreign ministry spokeswoman Maria Zakharova in a social media post late Monday described the comments as "beyond Russophobia," and "perversion".

"Not long ago the West thought it was the other way around -- that the Slavs were torturing Chechens, but now they've made a U-turn," she said, referring to two Russian wars in the southern republic of Chechnya.

The Free Buryatia Foundation, an advocacy group that speaks out against the conflict in Ukraine also criticised the Pope's comments.

"Stereotypes remain stereotypes no matter who replicates them: activists, politicians, or spiritual leaders. And the Pope's remarks about cruel Buryats and Chechens are not only racist stereotypes, but also lies," it said in a statement on social media.