vatican city pope francis appear harden catholic church teach nuclear weapons friday say countries stockpile even purpose deterrence remark start disarmament conference bring 11 nobel peace prize winners vatican appear go previous popes say nuclear weapons never use hold arsenals solely deter countries use could morally acceptable step toward achieve nuclear-free world address group 16th century fresco clementine hall vatican apostolic palace francis speak catastrophic humanitarian environmental effect employment nuclear devices add also take account risk accidental detonation result error kind threat use well possession firmly condemn tensions unite state north korea increase pope often warn nuclear conflict would destroy good part humanity call third country mediate dispute address francis directly mention north korea tension speak general climate instability conflict mentality fear world today international relations hold captive military force mutual intimidation parade stockpile arm say also say international laws proliferation nuclear weapons keep new state acquire money use develop modernize weapons instead spend help poor protect environment douglas roche canada former ambassador disarmament former senator tell conference pope remark possession nuclear weapons historic ask national conferences catholic bishops work make know another participant suggest pope write encyclical letter address catholics moral imperative ban nuclear weapons among meet pope beatrice fihn executive director international campaign abolish nuclear weapons ican mohamed el baradei director general emeritus international atomic energy agency iaea fihn whose group nobel year tell reuters ask pope lead 1.2 billion catholics around world prayer end threat nuclear weapons sunday december 10 group due collect prize tensions really high risk nuclear weapons use high height cold war cuban missile crisis think really serious need urgently something say el baradei peace prize 2015 ask would respond u.s. president donald trump threat use unprecedented fire fury north korea threaten unite state go pray say pope change predecessors condemn nuclear arsenals deterrence