During an attempt to cross the Siversky Donets River on May 11, the Russian army lost 485 servicemen and damaged more than 80 units of equipment.
This was reported by the Institute for the Study of War.
U.S. analysts say Russian troops made significant tactical mistakes in attempting a large-scale crossing of the river near Kreminna town.
According to researchers, the Russian command sent 550 servicemen from the 74th Motorized Rifle Brigade of the 41st All-Army to force the Siversky Donets to surround Ukrainian troops near Rubizhne.
On May 11, Ukrainian artillery destroyed Russian pontoon bridges and densely packed troops and equipment.
The Institute for the Study of War notes that on March 8, the 74th Motorized Rifle Brigade had already tried to cross the Desna River in Chernihiv Oblast and had failed to do so.
"The command and headquarters of the unit may not have realized the danger posed by the improvement of Ukraineʼs artillery capabilities in two months, or simply were incompetent or unable to control their troops," — say US researchers.