U.S. official : Tens of thousands of Russian soldiers along border have been moving back . Acting president says Russian grenade launcher downed helicopter . Donetsk mayor says he is in talks with separatist leaders , aims to calm situation . Taruta has met with Poroshenko in Kiev , he said , adding that the President-elect will visit the Donetsk region `` we hope in the first half of June . '' Self - declared separatist leader of Ukraine says militants have 4 missing OSCE monitors .
U.S. official : Tens of thousands of Russian soldiers along border have been moving back . Acting president says Russian grenade launcher downed helicopter . Donetsk mayor says he is in talks with separatist leaders , aims to calm situation . Self - declared separatist leader of Ukraine says militants have 4 missing OSCE monitors .