In a tweet that gained wide notice internationally, President Donald Trump warned that an Iranian attack on U.S. targets could drive him to counter with an attack on Iranian cultural sites.

Just days after he ordered a drone strike that killed high-ranking Iranian military figure Qassem Soleimani, Trump tweeted, "Let this serve as a WARNING that if Iran strikes any Americans, or American assets, we have.........targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD. The USA wants no more threats!"

....targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD. The USA wants no more threats! — Donald J. Trump (@realDonaldTrump) January 4, 2020

Trump later doubled down, telling reporters aboard Air Force One, "They’re allowed to kill our people. They’re allowed to torture and maim our people. 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."

Iran has 24 sites on UNESCO’s World Heritage List, and an additional 56 proposed sites that could be eligible in the future. Iran is home to the Shia religious centers of Mashhad and Qom; a landmark 5th Century B.C. hydraulic system; a variety of seminal landscaped gardens; and Persepolis, the onetime capital of the Persian Empire.

"At three times the area of France, Iran is vast, and its cultural history dates back millennia," said Stephennie Mulder, associate professor of Islamic Art at the University of Texas-Austin.

Critics quickly warned that a deliberate attack on cultural sites could mean that Trump and other officials are committing war crimes.

The critics have a good argument, but enforcement would hardly be a certainty. Let’s take a closer look.

What laws govern attacks on cultural sites?

The legal framework for protecting cultural sites is extensive.

"The purposeful targeting of cultural sites is prohibited and is punishable under international law according to multiple statutes," Mulder said.

The United States is a party to two significant international agreements that explicitly outlaw attacks on cultural sites: the Geneva Convention of 1949 and the Hague Convention of 1954.

The Geneva Convention for the Protection of Civilian Persons in Time of War, Article 53 (1949), said that members "shall refrain from any act directed by way of reprisals against cultural property."

Further, Article 147 would make such destruction — if extensive, wantonly undertaken and not militarily necessary — a "grave breach" of the Geneva Convention. This is important because a "grave breach" of the convention would make the offense a war crime, said Anthony Clark Arend, a professor of government and foreign service at Georgetown University and a specialist in international law.

"If the president intentionally targeted Iranian cultural sites in circumstances where there was no specific military necessity, he would be committing a war crime," Arend said.

In addition, Article 4 of the Hague Convention for the Protection of Cultural Property in the Event of an Armed Conflict, says the parties must "respect cultural property" and to protect it from "destruction or damage." The only exception is for "military necessity."

Meanwhile, an earlier agreement that the United States is a party to says that in sieges and bombardments, "all necessary steps must be taken" to spare historical monuments and buildings dedicated to religion, art, science, as long as they are not being used for military purposes.

In 2017, a few months after Trump took office, the United Nations Security Council unanimously passed a resolution that condemns the unlawful destruction of cultural heritage sites. It came in the wake of several high-profile incidents that drew international condemnation: -- the Taliban’s destruction of the monumental Buddha statues of Bamiyan, ISIS’ destruction of the ancient city of Nimrud in Iraq, and the demolition of Palmyra and other sites in Syria.

Similar language is included in Geneva Convention Protocol 1, article 53 and the Rome Statute of the International Criminal Court. The United States has signed these agreements, but they are not binding. The United States has not ratified them.

Perhaps most important, however, is an attack on cultural sites would violate U.S. law, not just international law.

Mulder said that any attack on a culture site would be a "clear infringement" of the U.S. War Crimes Act, which reads, "Whoever, whether inside or outside the United States, commits a war crime ... shall be fined under this title or imprisoned for life or any term of years, or both, and if death results to the victim, shall also be subject to the penalty of death."

And the Defense Department’s Law of War Manual makes clear that cultural property is to be protected. (The document mentions the phrase "cultural property" more than 600 times.)

The manual says that Defense Department personnel, "should act as if they were legally bound by the rules for the protection of cultural property in the 1954 Hague Cultural Property Convention during hostilities, even when conducting operations in the territory of a state that is not a party" to the convention.

How stringently have violations been prosecuted?

Enforcement of these rules has run hot and cold over the years.

Enforcement efforts languished after a flurry of prosecutions after World War II. Then, after the warfare in the former Yugoslavia in the 1990s, individuals were convicted and sentenced to prison by an international criminal tribunal for destroying cultural property, said Patty Gerstenblith, director of the DePaul University College of Law’s Center for Art, Museum and Cultural Heritage Law.

Cultural property advocates applauded the 2018 International Criminal Court conviction of a jihadist in Mali for destroying shrines and a mosque in Timbuktu.