The first US-born pontiff, speaking on a visit to France as a tense UN General Assembly unfolded in New York, also decried world leaders who disrespected the rule of law, without naming individuals.
"Instead of respecting the law, those in power invoke it when it serves their interests and disregard it when it restrains them, treating even justice itself as though it were a commodity to be bought and sold," the Pope said.
The UN and other multilateral groups "are experiencing a crisis of effectiveness", he said.
"Dialogue is seen as an obstacle to action rather than a resource for peace, a charade rather than an opportunity to seek the common good together."
Leo is on a whirlwind four-day, three-city visit to France, where he is seeking to repair the Church's standing there after abuse scandals.
The Pope, who has made sounding the alarm about the risks of artificial intelligence a central part of his 16-month papacy, put the issue at the heart of his visit to France.
Earlier on Friday, he urged the world to reconsider the development of AI, warning in a speech to French leaders that it could create a future where "a paradise of machines" takes control of the Earth.
"If we are to avoid losing our humanity amid a 'paradise of machines' invading and conditioning our daily lives, there is an urgent need for education in ethical discernment," he said, speaking under the gilded ceilings of the Elysee Palace.
The Pope was later greeted by enthusiastic crowds as he arrived at the restored Notre-Dame cathedral to lead a prayer service, in the first visit by a pontiff since a devastating fire nearly destroyed the Gothic masterpiece in 2019.
"The collective effort to rebuild it, and the splendour of the result reveal that the heart of a people beats here, and that here we stand at the living centre of a civilisation, where past and future embrace, where heaven and earth meet," he said.
France, a secular country where the separation of church and state is enshrined in a 1905 law, has witnessed a steady decline in affiliation to the Catholic Church during the post-war era, mirroring a trend in other traditionally Catholic countries.
Leo's visit comes as Catholic leaders in France have been at odds with the government over the 2024 enshrining of a right to abortion in the French constitution and the passage of the law legalising assisted dying for adults with incurable illnesses.
On Friday, the Pope strongly reiterated the Church's pro-life teachings, criticising initiatives to allow assisted dying for those who have incurable illnesses.
"I am concerned … by those trends in society that risk turning science and technology into profit-driven ventures promoting genetic manipulation, surrogacy, the trade in human organs or the possibility of arranging one's own death," he said.
