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Arestovych said that some of these forces have already been captured by the Ukrainian Armed Forces.
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"They have already joined the units defending Svatove, Lyman and Kupyansk," the Office rep stated.
"Some of them were killed, some are already in captivity. Everything is very fast. Their fate is sad because they are not allowed to prepare at all."
Read also: President's Office comments on prospects for additional mobilization in Ukraine
Putin announced a "partial mobilization" in Russia on Sept. 21. The call-up came after the Russian army suffered a heavy defeat in Ukraine, losing nearly the entirety of their occupied territory in Kharkiv Oblast.
Russian Defense Minister Sergei Shoigu announced that 300,000 reservists would be called up during this draft round.
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However, according to Russian opposition media, classified mobilization plans envisage sending one million Russians or more to war against Ukraine.
Military experts uniformly do not believe in the logistical or command capability of Russia to effectively corral that many troops.