As Russian troops continue to make advances across Ukraine, including the capital Kyiv, there are concerns that Belarus may step up its engagement by joining forces with the Russian side.

Russia's defense ministry said on Saturday that the Russian military has so far destroyed about 3,500 military facilities and vehicles during its invasion of Ukraine.

Russian troops are approaching Kyiv from three directions.

The defense ministry said Russia has also struck military airfields in Lutsk and Ivano-Frankivsk in western Ukraine with long-range missiles. The US Department of Defense is analyzing the strikes in the western region.

On Friday, Russian President Vladimir Putin met with the president of Belarus, Alexander Lukashenko, in Moscow, and stressed their countries' unity.

A spokesperson for Belarus's presidential office says the leaders have agreed that Russia will soon provide Belarus with state-of-the-art weapons.

Ukraine's air force said on Friday that Russian aircraft had attacked positions in Belarus near the Ukrainian border.

Belarus's defense ministry and border guards deny the allegation, but a senior official at Ukraine's presidential office said it could be a false-flag attack by Russia aimed at drawing Belarus into the conflict.

Observers say Russia apparently wants to get Belarus involved in the war so as to improve its situation.