Russia's defense minister has named a top uniformed military officer the overall commander for the nation's military operations in Ukraine.

Russia's Defence Ministry said on Wednesday that Sergei Shoigu appointed the armed forces' Chief of the General Staff Valery Gerasimov as commander of all troops fighting Ukraine.

It is rare for the Russian military's highest-ranking uniformed officer to take command of forces in an operation.

The ministry said the appointment is connected to expansion of the scale of tasks, the need to organize closer cooperation between branches of the armed forces and improving supplies.

Russian newspapers heralded the appointment with front-page headlines.

A leading daily noted that three top-ranking officers of Russia's army and Aerospace Forces were named deputies under Gerasimov's command.

It said all Russian forces will be deeply involved in the operation in Ukraine, and that the military reshuffle likely means a large-scale offensive against the country is imminent.

A US think tank, the Institute for the Study of War, says the change was necessary both to improve Russian command and control and to intensify the country's operations in Ukraine.

The institute also says it is likely that Gerasimov's appointment is partly aimed at signaling President Vladimir Putin's intent to fight a long war in Ukraine.

Ukrainians are on alert for possible heightened Russian attacks on the capital Kyiv and other cities early this year.