According to a declassified U.S. intelligence estimate, Russia has lost 315,000 soldiers to the war in Ukraine, or about 90% of its total force strength, according to a source with knowledge of the material on Tuesday.

According to the source, the assessment also determined that Russia’s military modernization has been delayed by eighteen years as a result of Moscow losing soldiers and armored vehicles to the military of Ukraine.

The Russian embassy did not immediately respond to a request for comment. Russian defense ministry and Kremlin officials could not immediately be reached for comment.

The source spoke as Ukrainian President Volodymyr Zelenskiy made a last-ditch plea to U.S. lawmakers on Capitol Hill to keep U.S. military aid flowing to Ukraine, first meeting behind closed doors with U.S. senators.

The source said the recently declassified U.S. 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.

The source said those losses are the reason Russia has been forced to loosen recruitment standards and draft convicts and older civilians to deploy in Ukraine.