US intelligence also said that more than 2000 Russian tanks have also lost since war began.
Some 315,000 Russian troops have been killed or wounded in Ukraine since the war began in February 2022, nearly 90 percent of its pre-war force, a congressional source said Tuesday.
The Russian military has also lost some 2,200 of the 3,500 tanks it had before the start of the conflict, the source said, citing a declassified US intelligence assessment shared with Congress.
The document emerged as Ukrainian President Volodymyr Zelensky was in Washington seeking to convince an increasingly skeptical Congress that the war with Russia could be won with continued US funding.
Zelensky met with congressional leaders on Tuesday before scheduled talks at the White House with President Joe Biden.
The latest casualty assessment marks a big leap from that provided in July 2022 when CIA director Bill Burns said US intelligence estimated that Russian losses were "in the vicinity of 15,000 killed and maybe three times that wounded."
Both Russia and Ukraine have been deeply reticent about providing casualty figures from the war.
Russian casualties of 315,000 killed or wounded would amount to 87 percent of the country's pre-war military force of 360,000.
The Wall Street Journal, citing the declassified US intelligence assessment, said the conflict in Ukraine "has sharply set back 15 years of Russian effort to modernize its ground force."
To make up for the heavy losses, Russia has resorted to "extraordinary measures" such has conscripting released prisoners and sending them to the front, it added.
Republican House Speaker Mike Johnson insisted after the meeting with Zelensky that his party would not approve Biden's request for $60 billion in fresh assistance for Kyiv unless Democrats meet their demands on immigration.
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