Pope Leo has criticised the “culture of power” behind the rapid expansion of artificial intelligence, warning that the technology must be held to “the most rigorous” ethical standards as it spreads across fields from employment to warfare.

In his encyclical, the first major document of his papacy focused on safeguarding humanity, he also issued an apology for the Catholic Church’s historical delay in condemning slavery, calling it “a wound in Christian memory.”

He further warned of “new forms of slavery” emerging from the digital economy.

Breaking with tradition, Leo personally presented the document on Monday at a Vatican event.

Attendees included Christopher Olah, a co-founder of US-based AI company Anthropic, which is currently involved in a legal dispute with the Trump administration over AI ethics.

Encyclicals are among the most authoritative teaching documents issued by a pope to the Catholic Church’s 1.4 billion members, typically setting out papal priorities and addressing major social and moral issues.

In the encyclical titled Magnifica Humanitas (“Magnificent Humanity”), Leo, the first US-born pope, originally from Chicago—warned of what he described as a “troubling revival of war as an instrument of international politics.”

He also argued that artificial intelligence is contributing to the “normalisation of war,” raising concerns about its growing role in modern conflict.

“For this reason, the development and use of AI in warfare must be subject to the most rigorous ethical constraints, to guarantee respect for human dignity and the sanctity of life and to avoid a race to develop such arms,” he wrote.

Leo called for the “disarming” of artificial intelligence, warning that certain autonomous weapons systems are now “practically beyond any human reach” to effectively control or regulate.

“Disarming AI means freeing it from the mentality of ‘armed’ competition,” he wrote.

“Disarming AI means freeing it from the mentality of ‘armed’ competition,” he wrote. “To disarm does not mean rejecting technology, but preventing it from dominating humanity,” adding that the technology should be “human-friendly”, accessible to all and opened to discussion and debate.

He explained that “disarming” AI means freeing it from a mindset shaped by armed competition. “To disarm does not mean rejecting technology, but preventing it from dominating humanity,” he wrote, adding that AI should remain “human-friendly,” widely accessible, and open to public discussion and debate.