According to US estimates, more than 20,000 Russian soldiers have been killed fighting in Ukraine since December.
National Security Council spokesman John Kirby said another 80,000 were injured, citing new classified information.
Half of the dead belong to the Wagner mercenary company, which is attacking the eastern city of Bakhmut.
Russia has been trying to wrestle the small city into a war of occupation for the past year.
Moscow currently controls most of Bakhmut, but Ukrainian troops still hold a small part of the city in the west. The intense fighting has assumed great symbolic importance for both sides.
Ukrainian officials have also said they are using the war to kill as many Russian troops as possible and deplete its reserves.
“An attempt by Russia to invade the Donbass [region] through Bakhmut has failed,” Mr. Kirby told reporters. “Russia has failed to capture any real strategic and important territory.
“We estimate that Russia has suffered over 100,000 casualties, including over 20,000 killed in action,” he added.
According to JEE News, losses in Bachmouth have been counted since the beginning of December.
“The bottom line is that after months of fighting and extraordinary losses, the Russian offensive has failed,” Mr. Kirby said.
He added that he was not giving an estimate of Ukrainian casualties because “they are the victims here. Russia is the aggressor”.
JEE News was unable to independently verify the figures and Moscow had no comment.
The capture of the city would move Russia closer to its goal of controlling the entire region of Donetsk, one of four regions in eastern and southern Ukraine annexed by Russia last September after a referendum. It was widely condemned abroad.
Bakhmut has little strategic value, analysts say, but it has become a focal point for Russian commanders, who have struggled to convey any positive news to the Kremlin.
The Wagner mercenary group – which uses criminals on a large scale and is notorious for its often inhumane practices – has become the centerpiece of the Russian attack on Bakhmut.
Its leader, Yevgeny Prigozhin, has staked his reputation and that of his private army on capturing the city.
But he had recently threatened to withdraw his troops from Bakhmut.
In an unusually in-depth interview with a prominent Russian war blogger, he vowed to withdraw the Wagner fighters if the Russian Ministry of Defense did not provide them with much-needed ammunition.
He warned that Wagner fighters could be redeployed to Mali.
He has frequently clashed with Russia’s Defense Ministry during the war, accusing officials of not providing enough support to its fighters.
Mr Prigozhin also called on the Russian media and military leadership to “stop lying to the Russian population” ahead of Ukraine’s expected spring retaliation.
“We need to stop lying to the Russian population, telling them everything is fine,” he said.
He praised the “good, accurate military action” and command of the Ukrainian army.
A top Ukrainian general said Monday that counterattacks had driven Russian forces from some positions in Bakhmut, but the situation remained “difficult.”
The commander of Ukraine’s ground forces, Gen. Oleksandr Serskyi, said in a telegram that new Russian units, including paratroopers and Wagner fighters, were “continuing to be thrown into battle” despite suffering heavy losses.
“But the enemy is unable to capture the city,” he said.
