The 35th Combined Arms Army was almost completely destroyed by the Ukrainians in Izyum.
The claim was made in a post on the Telegram channel.
The Institute for the Study of War cited a Russian military blogger who appeared to corroborate the claims in their assessment of the Russian invasion.
Russian commanders did not account for combat challenges in the Izyum woods, which resulted in significant losses for several brigades, according to the author of the book.
He claimed that the 64th and 38th Separate Guard Motor Rifles, which are part of the 35th Combined Arms Army, have less than 100 servicemen.
Insider has been unable to verify the claims.
Russian commanders didn't give the units with the equipment needed to fight in the woods and didn't repair their cannons quickly enough, according to a post on the website.
The units suffered from a lack of secure communication devices, which has been a problem for the Russian military throughout the war.
Ukrainian forces were able to strike Russian positions with drones because of the lack of communication.
Izyum has been occupied by Russian forces.
According to Iryna Venediktova, the commander of the 64th Motorized Rifle brigade ordered his soldiers to kill civilians.
In a post on Facebook, Venediktova claimed that she was responsible for violating the laws and customs of war and murder.
The 64th Motorized Rifle brigade is alleged to have been attacked by a group of people.