Joint air force exercises by Russia and Belarus on Monday sparked concerns in Ukraine that Belarus could be planning to join the war as part of a new Russian assault.

While Belarus has not directly gotten involved in the war, Russia did use the country to launch its February invasion of Ukraine. Belarusian officials have maintained that they will not join the fighting.

But the joint exercises, slated to continue until Feb. 1, have renewed anxieties in Ukraine. The exercises will include joint air patrols, actions to support ground forces, air reconnaissance and transport flights, according to the Belarusian Defense Ministry. All of the country’s air bases and firing ranges will be involved in the exercises.

The coordination between Russia and Belarus comes as a Russian missile strike on an apartment building in the Ukrainian city of Dnipro killed at least 40 people, with many more still missing, according to Reuters.

“As of now, the fate of more than 30 people who could have been in the house at the time of the terrorists’ missile hit remains unknown,” Ukrainian President Volodymyr Zelensky said in his nightly address.

Russian missile strikes also hit Kyiv and other parts of Ukraine in recent days as part of the Kremlin’s aerial assault as the war closes in on its one-year anniversary in February.