Russian soldiers in Russia's Kursk region.Russian Defense Ministry Press Service photo via APA US think tank estimates Russia lost about 40 troops per square mile seized in Ukraine in 2024.Russia's losses in its invasion of Ukraine are thought to have soared toward the end of the year.A former Russian president's remarks suggest Russia added just enough troops to replace its losses.A US think tank on Tuesday estimated that Russia lost about 40 troops per square mile seized in Ukraine in 2024.The Institute for the Study of War, which has been tracking Russia's full-scale invasion of Ukraine, said it had seen geolocated evidence indicating that Russian forces advanced 4,168 square kilometers, or about 1,609 square miles, last year.In calculating Russia's rate of losses, it used a recent estimate from the Ukrainian military's commander in chief, Oleksandr Syrskyi, that 427,000 Russian troops had been killed or injured in 2024.The slowness of Russia's advance this year — its estimated territory seized is slightly less than the land area of Delaware — has been compared with the rapid gains Ukraine was able to make when it launched an offensive into the Russian region of Kursk in August.