seoul south korea president moon jae-in japanese prime minister shinzo abe agree monday pursue strong unite nations sanction north korea pyongyang sixth nuclear test day early south korea presidential spokesman say head state agree cooperate closely unite state share understand must powerful sanction pressure apply north korea presidential blue house spokesman park su-hyun tell media brief part agree push powerful u.n. sanction park say moon abe speak 20 minutes phone aim strong sanction draw north korea dialogue say moon abe agree pursue strong u.n. sanction north korea blue house