Graves of Russian Wagner mercenary group fighters are seen in a cemetery near the village of Bakinskaya in the Krasnodar region of Russia on January 22.Reuters

A version of this story appears in CNN’s What Matters newsletter. To get it in your inbox, sign up for free here.CNN — There’s a growing rift at the top of the Russian government between Vladimir Putin’s official military and the off-the-books mercenary force that has achieved some gains for Russia in Ukraine.The oligarch figurehead of the private military company Wagner Group, Yevgeny Prigozhin, has been openly critical of Russia’s military and its bureaucracy.Recruiting for tens of thousands of fighters in Russian jails, Wagner offers freedom and cash after a six-month tour.Videos of these prison yard pitches made by Prigozhin have been shared on social media, and prison-rights groups in Russia estimate 30,000 have taken up the offer, according to an excellent analysis of what we know about Wagner and Prigozhin by CNN’s Tim Lister. Read Lister’s story.Brutal tactics for its fighters. A Ukrainian assessment of Wagner tactics suggests the convicts are pushed to the front lines in a human wave. Wagner is using “convicts as cannon fodder to try and storm Ukrainian positions with almost no fire support,” as CNN’s Fred Pleitgen said in a video report he filed after talking to Ukrainian tank operators.Lister, Pleitgen and CNN’s Victoria Butenko wrote about Wagner’s tactics after seeing the Ukrainian assessment. The focus is on small groups of fighters – a dozen or fewer – guided by drones.

Deserters are said to be shot. The wounded are left behind on battlefields for hours, according to the assessment. Prisoners account for the bulk of Wagner’s casualties as they are pushed to storm Ukrainian positions. More experienced fighters with better equipment follow.

Key lines from their report:

Despite a brutal indifference to casualties – demonstrated by Prigozhin himself – the Ukrainian analysis says that Wagner’s tactics “are the only ones that are effective for the poorly trained mobilized troops that make up the majority of Russian ground forces.”

It suggests the Russian army may even be adapting its tactics to become more like Wagner, saying: “Instead of the classic battalion tactical groups of the Russian Armed Forces, assault units are proposed.” Read more about the Ukrainian assessment.

Gaining power over the Russian military. US officials have said Wagner appears to be dueling with Russia’s military for power in the Kremlin.