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 in just the past five months, the White House said on Monday, the latest measure of the vast 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 who had been killed in action. About half of those were mercenaries for the Wagner group, the paramilitary force founded by Yevgeny V. Prigozhin that recruited heavily from Russian prisons to bolster its ranks and carry out a brutal campaign around the eastern Ukrainian city of Bakhmut.

In November, Gen. 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 the losses have grown for Russia as it has sent waves of poorly trained recruits and convicts to the front lines in Ukraine’s east, where months of intense fighting has engulfed the area around Bakhmut, a city that has been central to Mr. Putin’s goal of seizing the Donbas region.

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

“Russia’s attempt at an offensive in the Donbas largely through Bakhmut has failed,” Mr. Kirby said. “Russia has been unable to seize any real strategic and significant territory.”

Estimating casualties is notoriously difficult. Moscow is believed to undercount those killed or injured on the battlefield, and Mr. Kirby did not provide specific details on how the United States had calculated Russia’s losses, except to say it involved corroborated intelligence.

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

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

“They are the victims here,” he said. “Russia is the aggressor.”