Pope Leo on Wednesday criticised the "illusory security" of the global nuclear deterrence system, in an appeal on the 80th anniversary of the United States dropping an atomic bomb on the Japanese city of Hiroshima at the end of the Second World War.

Leo, the first U.S.-born pope, said in his weekly audience that the destruction in Hiroshima, which killed about 78,000 people instantly, should serve "as a universal warning against the devastation caused ... by nuclear weapons."

"I hope that in the contemporary world, marked by strong tensions and bloody conflicts, the illusory security based on the threat of mutual destruction will give way to ... the practice of dialogue," said the pontiff.

While the Catholic Church for decades gave tacit acceptance to the system of nuclear deterrence that developed in the Cold War, Leo's predecessor Pope Francis changed the Church's teaching to condemn the possession of nuclear arms.

Francis, who died in April after a 12-year papacy, also strongly backed the U.N. treaty to ban nuclear weapons, which formally went into force in 2021 but has not gained support from any of the nuclear-armed nations.

Leo's appeal on Wednesday came hours after representatives from 120 countries, including the U.S., attended an annual ceremony in Hiroshima to mark the atomic bombing.

Among those attending the ceremony was a delegation of Catholic bishops from Japan, South Korea and the U.S. including Cardinals Blase Cupich of Chicago and Robert McElroy of Washington, D.C.

"We strongly condemn all wars and conflicts, the use and possession of nuclear weapons and the threat to use nuclear weapons," the bishops said in a joint statement on Wednesday.