More than 2,300 years ago, the Persian capital of Persepolis was burned by a foreign warrior in a fatal blow to the empire and its rich heritage. The ruins of the ancient city, in modern-day southwest Iran, could now be on President Trump’s target list of 52 sites he has threatened to attack as tensions escalated between Washington and Tehran.

Mr. Trump did not identify which places the United States might strike, as he warned on Twitter that he would order — 52 in all, one for each American who was held hostage for the duration of the Iranian Revolution takeover of the American Embassy in Tehran in 1979.

But he said on Saturday that some of the sites were “very high level & important to Iran & the Iranian culture.”

“Those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD,” he added. “The USA wants no more threats!”

On Sunday, Mr. Trump maintained the right to “quickly & fully strike back, & perhaps in a disproportionate manner” should Iran strike any American person or target. Later that day aboard Air Force One, he told reporters flying with him back to Washington that “they’re allowed to kill our people.”

“They’re allowed to torture and maim our people,” he added. “They’re allowed to use roadside bombs and blow up our people. And we’re not allowed to touch their cultural site? It doesn’t work that way.”