Pope Francis on Friday urged countries not to stockpile nuclear weapons, even for the purpose of deterrence.
During a Vatican conference aimed at gathering support for nuclear disarmament, Francis said nuclear deterrence policies give a "false sense of security."
His remarks appeared to go further than those of previous popes, who have said that while nuclear weapons should never be used, stockpiling them to deter other countries' use of weapons could be morally acceptable.
Francis spoke to 11 Nobel Peace Prize winners who attended the conference, along with diplomats and government officials from around the world.
"International relations cannot be held captive to military force, mutual intimidation and the parading of stockpiles of arms,'' he said.
The pope said any use of nuclear weapons, even accidental, would be "catastrophic" for humanity and the environment.
The Vatican conference came amid mounting tensions between the United States and North Korea. In his address, Francis did not mention any conflict in particular but spoke of a "climate of instability and conflict" in the world today and a "mentality of fear."
He said peace and security between nations must be "inspired by an ethics of solidarity" rather than the stockpiling of arms.
The pope endorsed a new U.N. treaty that calls for the elimination of atomic weapons. None of the world's nuclear powers have signed the accord, arguing that its lofty ideals are unrealistic.
