Pope Leo warned of the risk of democracies sliding into “majoritarian tyranny” on Tuesday, in a letter issued by the Vatican two days after U.S. President Donald Trump attacked the pontiff on social media.

The first U.S. pope, writing to participants of a Vatican meeting about the use of power in democratic societies, said democracies remained healthy only when they were rooted in moral values.

“Lacking this foundation, (democracy) risks becoming either a majoritarian tyranny or a mask for the dominance of economic and technological elites,” said Leo in the letter.

The text, released as the pope was undertaking an ambitious, 10-day tour of four African countries, did not directly address the U.S. or name any specific democracies.

Trump sharply criticized Leo as “terrible” on Sunday night, after the pope had emerged in recent weeks as a growing critic of the U.S.-Israeli war on Iran.

Leo told Reuters on Monday that he planned to keep criticizing the war, despite Trump’s comments.

In Tuesday’s letter, the pope said the Catholic Church taught that power could not be seen as an end in itself “but as a means ordered toward the common good”.

“This implies that the legitimacy of authority depends not on the accumulation of economic or technological strength, but on the wisdom and virtue with which it is exercised,” said Leo.

The pope also urged leaders in democratic societies to avoid any temptation to hoard power.

“Temperance … proves essential for the legitimate use of authority, for true temperance restrains inordinate self-exaltation and acts as a guardrail against the abuse of power,” he said.

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(Reporting by Joshua McElwee; Editing by Alex Richardson)