Most of the fatalities are from the Wagner mercenary company, which has been attacking the eastern city of Bakhmut.

The small city has been the focus of a grinding war of attrition, with Russia attempting to take control since last year.

Although Moscow holds most of the city, Ukrainian forces still control a small portion in the west.

The battle holds significant symbolic importance for both sides, with Ukrainian officials using it as an opportunity to weaken Russia's reserves.

“Russia's attempt at an offensive in the Donbas largely through Bakhmut has failed. Russia has been unable to seize any real strategic and significant territory," Kirby told reporters.

“We estimate that Russia has suffered more than 100,000 casualties, including over 20,000 killed in action,” he added.

The US figures only account for losses since December, and Kirby noted that he was not providing estimates of Ukrainian casualties as Russia is the aggressor, and Ukrainians are the victims of the conflict. (ILKHA)