A US think tank says Russia's decision to appoint a former economic minister as defense minister suggests the country is preparing for prolonged conflict in Ukraine.

Russian President Vladimir Putin proposed on Sunday that Defense Minister Sergey Shoigu be replaced by First Deputy Prime Minister Andrey Belousov, an expert in economic policy.

The think tank, the Institute for the Study of War, wrote that Belousov's experience in managing various defense industrial base innovation and drone projects makes him suitable to lead the struggling Russian defense ministry.

It also pointed out that Putin is taking significant steps toward mobilizing the Russian economy and defense industrial base to support a protracted war in Ukraine and possibly prepare for a future confrontation with NATO.

Russian forces entered the eastern Ukrainian region of Kharkiv from the north. They say they had placed nine communities in the region under Russian control by Sunday.

The governor of Kharkiv says about 4,000 residents evacuated in two days.

Meanwhile, Russian officials said that in the western Russian province of Belgorod, bordering Kharkiv, Ukrainian shelling caused an apartment building to collapse on Sunday. The governor of Belgorod says 19 people were killed.