Pope Leo on Thursday decried political leaders who invoke religious beliefs to justify conflicts or nationalist policies, calling that a form of blasphemy, or a serious sin that disrespects or insults God.

Leo, the first U.S. Pope, did not name specific leaders in the message released ahead of the Catholic Church's World Day of Peace, celebrated on Jan. 1, but called on religious believers to resist any such uses of faith.

"Unfortunately, it has become increasingly common to drag the language of faith into political battles, to bless nationalism, and to justify violence and armed struggle in the name of religion," said the Pope.

"Believers must actively refute, above all by the witness of their lives, these forms of blasphemy that profane the holy name of God," he said.

Leo also warned against the use of artificial intelligence in warfare in the four-page message, issued annually by the leader of the 1.4 billion member Church.

"There is ... a growing tendency among political and military leaders to shirk responsibility, as decisions about life and death are increasingly 'delegated' to machines," he said.

"This marks an unprecedented and destructive betrayal of the legal and philosophical principles of humanism that underlie and safeguard every civilisation."

Leo, elected by the world's cardinals in May to succeed the late Pope Francis, has spoken several times in his first year about the challenges posed by AI.

He also condemned violence in the name of religion on his first overseas trip as Pope, telling Christian leaders across the Middle East during a trip to Turkey last month they must "strongly reject the use of religion for justifying war, violence, or any form of fundamentalism."

In the new message, the Pope also lamented a global increase in military expenditures, citing figures from the Stockholm International Peace Research Institute that worldwide military outlays increased 9.4% in 2024, reaching a total of $2.7 trillion, or 2.5% of global GDP.

Leo warned against a "confrontational logic (that) now dominates global politics, deepening instability and unpredictability day by day."