Russias Wagner mercenary fighters have arrived in neighboring Belarus as part of an agreement with the Kremlin, Ukrainian and Polish officials confirmed over the weekend.Minsksaid Friday that Wagner mercenaries were acting as military instructors for Belarusian territorial defense forces, three weeks after the group's aborted mutiny in Russia."As of now, available information shows that separate groups of representatives from private military companies [Wagner] have begun to be observed in Belarus moving from the territory of Russia,"said Andriy Demchenko, Ukraines State Border Guard Service spokesman.The Ukrainian border service said in a statement on the Telegram messaging app Sunday that it was working to determine the Wagner fighters location and their numbers.Meanwhile, Polands Deputy Minister Coordinator of Special Services, Stanislaw Zaryn, estimated the number of Wagner mercenaries in Belarus at several hundred.These Russian criminals and thugs are now set to train the Belarusian army and settle in locations that have been prepared for them, Zaryn tweeted Sunday.Wagner was allowed to recruit fighters from across Russian prisons last year, with President Vladimir Putin personallypardoning inmates after their six-month service.A number of Wagner fighters have been seen in Belarus since Tuesday, Reuterscited two anonymous sources close to the mercenaries as saying.The reports coincided withvideos of columns of vehicles with Wagner markings crossing into Belarus.