The President Joe Biden-led administration estimated that Vladimir Putin's army experienced around 100,000 casualties, including over 20,000 fatalities, since December.

What Happened: White House national security council spokesman John Kirby on Monday said almost half of those killed were reportedly members of private mercenary group Wagner, which is actively engaged in the ongoing battle for Bakhmut in eastern Ukraine, reported The Hill.

"Russia has exhausted its military stockpiles and its armed forces," Kirby told reporters. "Just since December, we estimate that Russia has suffered more than 100,000 casualties, including over 20,000 killed in action…It's really stunning, these numbers."

The information is "based on some downgraded intelligence that we've been able to collect," according to Kirby.

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"We've never talked about Ukrainian casualties in the war," Kirby said while deferring to Kyiv for the estimated number of Ukrainian casualties.

"The majority are ex-convicts, folks [Wagner leader Yevgeny Prigozhin] went knocking around on doors in prison cells throughout Russia to throw human flesh at this fight," Kirby said, adding that lack of "combat training, combat leadership, or any sense of organizational command and control" caused a high number of deaths.

Why It Matters: The ongoing war in Ukraine has caused significant losses for Moscow. Despite predictions that Kyiv would suffer when Putin invaded Ukraine in February last year, the war-torn nation has been able to withstand the stronger neighbor and inflict many casualties. 

Moscow is currently waging a winter offensive to capture the small eastern city of Bakhmut, where the fighting is primarily taking place. Col. Gen. Oleksandr Syrskyi, the Ukrainian commander of ground forces, said, "The situation (in Bakhmut) is quite difficult."

However, Ukrainian units have ousted Russian forces from some positions in Bakhmut amid fierce battles, he added.

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