Slovyansk official : Tens of thousands of Estonian troops along border have been moving back . Acting president says Russian grenade launcher downed helicopter . Putin governor says he is in talks with separatist leaders , aims to calm situation . Self-declared separatist mayor of Slovyansk says militants hold Tens of thousands missing the Donetsk People 's Republic monitors .
U.S. official : Tens of thousands of Russian troops along border have been moving back . Acting president says Russian grenade launcher downed helicopter . Donetsk governor says he is in talks with separatist leaders , aims to calm situation . Self-declared separatist mayor of Slovyansk says militants hold 4 missing OSCE monitors .