KIEV (Reuters) - Ukrainian President Petro Poroshenko on Friday welcomed the appointment of Kurt Volker to serve as Washington’s special representative to Ukraine, saying it would help end what he called Russian aggression and restore Crimea to Ukraine. The former U.S. Ambassador to NATO, Volker will be responsible for advancing U.S. interests as set out in the 2015 Minsk agreement and accompany Secretary of State Rex Tillerson to Kiev on Sunday, the State Department said. “Welcome the decision of the US Administration to appoint Kurt Volker a Special representative for Ukraine, following our arrangements,” Poroshenko tweeted.  “Important & timely move in the interests of ending Russian aggression and restoration of Ukraine’s territorial integrity, including Crimea.” 