Russia has suffered more than 100,000 casualties since December and the "stunning" number is a key signal that Moscow's winter offensive has “backfired,” according to new estimated figures announced by the Biden administration on Monday.

White House official John Kirby told reporters Russia has "exhausted its military stockpiles and its armed forces" and the US estimates more than 20,000 of its troops have been killed in action in recent months.

The US is defining the term “casualty” as both wounded and killed.  

Kirby, who serves as National Security Council coordinator for strategic communications, noted that “nearly half” of those casualties were fighters with the Russian private company Wagner — whom CNN has reported have experienced horrific experiences on the battlefield following minimal training and little leadership.

Kirby lambasted a recent assertion from Wagner leader Yevgeny Prigozhin, who said Sunday that his group had only suffered 94 casualties. Kirby called Prigozhin's comments “just a ludicrous claim.” 

Pressed on the source of the new 100,000 figure, Kirby said it was “based on some downgraded intelligence that we’ve been able to collect.” He declined to provide information on Ukrainian casualties, noting that the US has “never” provided such information and would defer to Ukraine on the matter.

Kirby added that the Ukrainians “are the victims here, Russia is the aggressor, and I'm simply not going to put information in the public domain that's going to, again, make it any harder for the Ukrainians."

The official noted that it's ultimately Ukraine's decision to declassify the information and make their casualty figures public. "I don't need to abide by that same sense of courtesy for the Russians — haven't done it and I ain't going to start now," he said.

With regards to fighting on the ground, Kirby said “most” of Russia’s efforts have “stalled and failed” as the battle for the eastern city of Bakhmut continues. He added that Russia has made “incremental” gains in the town that has “very little strategic value.” 

“The bottom line is that Russia's attempted offensive has backfired. After months of fighting and extraordinary losses, Russia continues to be focused on a single Ukrainian city with limited strategic value," the official said.

Kirby said any decision about a spring counteroffensive from Ukraine would be “for President (Volodymyr) Zelensky to make,” but the US will continue to provide military aid and support. 

The US official also told reporters a future package for Ukraine would be unveiled "very soon."

"What we want to stay focused on is making sure that we're helping them be as ready as they can be for whenever they choose to step off. And that means, obviously, in material support,” he told reporters.