"A diplomacy that promotes dialogue and seeks consensus among all parties is being replaced by a diplomacy based on force, by either individuals or groups of allies.

"War is back in vogue and a zeal for war is spreading," said the first US pope.

Leo warned that the principle established after the Second World War, "which prohibited nations from using force to violate the borders of others, has been completely undermined".

"Peace is sought through weapons as a condition for asserting one's own dominion. This gravely threatens the rule of law, which is the foundation of all peaceful civil coexistence," he said.

The pontiff pointed to the "weakness of multilateralism" as "a particular cause for concern at the international level".

He said adhering to international humanitarian law was "a commitment that States have made", and such law "must always prevail over the ambitions of belligerents".

"We cannot ignore that the destruction of hospitals, energy infrastructure, homes and places essential to daily life constitutes a serious violation of international humanitarian law," he said.