President Donald Trump doubled down on threats to Iranian cultural sites on Sunday, warning that he considered them fair targets as tensions escalate following the Trump-ordered assassination of Tehrans top military general Qassem Soleimani last week.

Theyre allowed to kill our people. Theyre allowed to torture and maim our people. Theyre allowed to use roadside bombs and blow up our people. And were not allowed to touch their cultural sites, Trump said aboard Air Force One as he returned to Washington from a two-week vacation at his Mar-a-Lago resort in Florida. It doesnt work that way.

He made similar comments on Twitter on Saturday, when he announced that 52 Iranian sites could be targeted, some at a very high level & important to Iran & the Iranian culture.

Whatever Trump thinks constitutes a legitimate target, it isnt clear the military agrees.

In a Monday afternoon interview on CNN , Defense Secretary Mark Esper repeatedly affirmed the U.S. will follow the laws of armed conflict when asked if he was willing to target cultural sites.

Targeting cultural sites is illegal under the 1954 Hague Convention and the 1972 World Heritage Convention , which both the U.S. and Iran have ratified . And as Iranian Foreign Minister Mohammad Javad Zarif noted in a tweet of his own, the destruction of cultural landmarks is reminiscent of ISIS fighters, who destroyed countless ancient Christian and Muslim holy sites as they took over Syria and Iraq.

On Monday, White House adviser Kellyanne Conway attempted to bolster the legality of Trumps threat by implying that some of Irans military sites have cultural importance. I think that Iran has many military, strategic military sites that you may cite are also cultural sites, she told reporters.

Its unlikely that argument will win over U.S. allies and international nonprofits, however, who have recoiled at Trumps repeated threats.

Iran houses 24 UNESCO World Heritage sites , the designation given to irreplaceable natural and cultural monuments around the world. UNESCO Director-General Audrey Azoulay called for their protection Monday, hailing the sites as vectors of peace and dialogue between peoples, which the international community has a duty to protect and preserve for future generations.