Ukraine's defense minister said on Tuesday that Russia could prepare an attack force in Belarus to launch a new offensive on Ukraine, but that he hoped Minsk's troops wouldn't take part.  Defense Minister Oleksii Reznikov and other Ukrainian officials have suggested Moscow could attempt a winter offensive after mobilizing more troops.  A visit to Belarus by Russian President Vladimir Putin on Monday also increased speculation abroad that Moscow wants its ally to play a more direct role in the war in Ukraine.  Reznikov told Ukrainian television there was no evidence that Russia had already begun assembling an offensive-ready combat force in Belarus, which borders both Russia and Ukraine, or that Minsk would be dragged into the war.  "I think it's not in the interests of the leadership of Belarus to waste its military potential," Reznikov told Ukrainian television. "So I have hope that they will continue holding this balance."  Russian forces used Belarus as a launch pad for an abortive attack on Kyiv in February but Minsk has not joined the war directly or sent its own troops into battle in Ukraine.  Reznikov spoke after another Ukrainian general said Russian aircraft were training in Belarusian airspace to identify targets in Ukraine for potential missile strikes.  "Accordingly, we are taking all measures to lower the threat level," joint forces commander Serhiy Nayev said.  Ukrainian officials say Russian forces have continued using airfields in Belarus to launch attacks on Ukraine since the Feb. 24 invasion.