Russia's defense ministry says defense minister Sergei Shoigu has appointed Chief of the General Staff Valery Gerasimov to oversee what the country calls the special military operation in Ukraine.
It also said Sergei Surovikin, commander since October, and two other senior officers will be subordinate to Gerasimov.
The ministry says the new appointments are related to the "broader scope of tasks" and the need for closer coordination between all military branches and services.
It is unusual for the chief of staff, the top uniformed officer of the Russian military, to take command on his own.
Amid reports of discord between Russian regular forces and private military company Wagner Group, the move is believed to be aimed at clarifying the chain of command and better controlling troops.
Fierce fighting continues around the Ukrainian stronghold of Bakhmut in the east of the country. Russian military leaders told domestic media on Wednesday that the whole town of Soledar is now under their control.
Ukrainian President Volodymyr Zelenskyy said on Wednesday that what he called a terrorist state is "trying to pretend that some part of our city of Soledar -- a city that was almost completely destroyed by the occupiers -- is allegedly some kind of Russia's achievement."
Ukraine is stepping up its vigilance, suspecting that Russian forces plan to launch another large-scale attack on the capital, Kyiv, early this year.