A declassified US intelligence report assessed that the Ukraine war has cost Russia 315,000 dead and injured troops, or nearly 90% of the personnel it had when the conflict began, a source familiar with the intelligence said, Report informs referring to Reuters.

The report also assessed that Moscow's losses in personnel and armored vehicles to Ukraine's military have set back Russia’s military modernization by 18 years, the source said.

The Russian embassy referred a request for comment to the Russian defense ministry in Moscow. The ministry did not respond to requests for comment.

Russian officials have said Western estimates of Russian death tolls in the war are vastly exaggerated and almost always underestimate Ukrainian losses, which Russian officials say are vast.

The source spoke as Ukrainian President Volodymyr Zelenskyy made a last-ditch plea for more military aid to US lawmakers on Capitol Hill, where he faced a skeptical reception from key Republicans.

At a news conference later in the day, US President Joe Biden reaffirmed continued support to Zelenskyy, and warned lawmakers they risked handing a victory to Russia.

The source said the recently declassified US intelligence report assessed that Russia began its full-scale invasion of Ukraine in February 2022 with 360,000 personnel.

Since then, the report found, 315,000 Russian troops, or about 87% of the total with which it started the war, have been killed or injured, the source said.

Those losses are the reason Russia has loosened recruitment standards for deployment in Ukraine, the source added.

"The scale of losses has forced Russia to take extraordinary measures to sustain its ability to fight. Russia declared a partial mobilization of 300,000 personnel in late 2022, and has relaxed standards to allow recruitment of convicts and older civilians," the assessment said, according to the source.