U.S. officials are increasingly concerned that the private military contractor Wagner is becoming the predominant Russian military force in the eastern part of Ukraine.
For weeks, U.S. officials have been tracking the movements of people and weapons associated with Wagner — a paramilitary group with known ties to the Russian state — in the beleaguered city of Bakhmut. The group has taken over command of some of the Russian operations in parts of the Donbas region, according to a...