Mr. Graham, a retired military lawyer in the Air Force Reserve, said he delivered that message to Mr. Trump in a telephone call on Monday. “I think the president saying ‘we will hit you hard’ is the right message,” he said. “Cultural sites is not hitting them hard; it’s creating more problems. We’re trying to show solidarity with the Iranian people.”
Senator Jack Reed, Democrat of Rhode Island and a member of the Senate Armed Services Committee, said Mr. Trump’s threats would only encourage despots of the world to target antiquities themselves.
“America is better than that, and President Trump is flat-out wrong to threaten attacks on historic places of cultural heritage,” said Mr. Reed, a former platoon leader in the Army’s 82nd Airborne Division. “Destroying some of these culturally significant Iranian sites wouldn’t be seen as just an attack against the regime in Tehran, it could be construed as an attack on history and humanity.”
Iran, home to one of the world’s most storied ancient civilizations, has 22 cultural sites designated on the World Heritage List by UNESCO, the United Nations cultural organization, including the ruins of Persepolis, the capital of the Achaemenid Empire later conquered by Alexander the Great. Others include Tchogha Zanbil, the remnants of the holy city of the Kingdom of Elam, and a series of Persian gardens that have their roots in the times of Cyrus the Great.
The United States is a signatory to a 1954 international agreement to protect cultural property in armed conflict and has been a leader in condemning rogue nations and groups that destroy antiquities, including the Islamic State’s destruction of sites in Mosul, Iraq, and Palmyra, Syria, and the Taliban’s demolition of the famed Bamiyan Buddhas in Afghanistan in 2001.
Experts said that what Mr. Trump described would likewise violate international law. “We and others accused ISIS of war crimes when they did this,” said Jeh C. Johnson, a former secretary of homeland security under President Barack Obama who previously served as the top lawyer at the Pentagon. “Certainly, in aggravated circumstances, it should be considered a war crime.”
Mr. Johnson and others said there could be situations that are murkier, if the actual cultural value was less clear or it was being used as a military facility. Still, Mr. Johnson said, “my guess is his national security lawyers did not vet that tweet.”