The White House did not divulge any estimate of Ukraine’s losses.

At least 100,000 Russian fighters have been killed or wounded in Ukraine just five months ago, the White House said on Friday, the latest measure of the human toll of President Vladimir V. Putin’s invasion.

John Kirby, a spokesman for the National Security Council, said the figure included 20,000 Russian fighters killed in action. About half of them were mercenaries for the Wagner group, a paramilitary force founded by Yevgeny V. Prigozhin who recruited many from Russian prisons to bolster its ranks and wage a brutal campaign in the eastern Ukrainian city of Bakhmut.

In November, General Mark A. Milley, the chairman of the Joint Chiefs of Staff, reported that 100,000 fighters on each side had been killed or wounded since the war began in February 2022. American officials believe that the losses have increased for Russia. has sent waves of poorly trained recruits and convicts to the front lines in eastern Ukraine, where months of fierce fighting have engulfed the region around Bakhmut, a town central to Mr Putin’s goal of retaking the Donbas region.

While both sides have fought bitterly over Bakhmut, military analysts have suggested that control of the city has more symbolic power than strategic importance.

“Russia’s attempts to attack the Donbas largely through Bakhmut have failed,” Mr. Kirby said. “Russia cannot seize strategic and important territory.”

Estimating casualties is very difficult. Moscow is believed to undercount the number of people killed or wounded in the battle, and Mr. Kirby did not give specific details about how the United States has calculated Russian losses, except to say that it involves corroborated intelligence.

A trove of leaked Pentagon documents disclosed in April included American estimates that in February Russia had sustained between 189,500 and 223,000 casualties, including up to 43,000 killed in action. The document also estimates that Ukraine has suffered 124,500 to 131,000 casualties, of which 17,500 were killed in action.

Kyiv has also been reluctant to disclose information on war losses and Mr. Kirby did not provide any updates on Ukrainian casualties there.

“He’s the victim here,” he said. “Russia is the aggressor.”