BAGHDAD — The United States handed over more than 400 ancient artifacts to Iraq on Wednesday, part of ongoing efforts to repatriate the country’s looted heritage. But this latest batch has a particularly intriguing back story — the antiquities were seized by U.S. Special Operations forces members as they raided the house of a leader of the Islamic State militant group.

The nighttime operation to capture the militant took place in eastern Syria in May, and the Delta Force troops did not come back with their prize. It was their first such ground mission in the country, and their main target, a man known as Abu Sayyaf who ran oil operations for the Islamic State in the area, was killed in an ensuing firefight.

But as the commandos scoured the compound for documents and laptops that could provide intelligence about the organization, they stumbled across artifacts thought to be dating back as far as 4,000 years.

Among them was a religious text written in Aramaic, the ancient Semitic language said to have been spoken by Jesus. An official at the National Museum of Iraq in Baghdad said Wednesday that it was about 500 years old but has not yet been properly dated. (Museum officials also said that, as with many of the items found, they could not be sure whether the text was of Syrian or Iraqi origin.)

There were hundreds of coins — some of them gold from the Abbassid era, others silver pieces from the Umayyad period. There were stone cylindrical seals from the ancient city of Nimrud and fragments of pottery.

The presence of the artifacts in Abu Sayyaf’s house is perhaps not surprising. The Islamic State’s “Diwan al-Rikaz” — a ministry overseeing precious resources — has departments in charge of both oil and gas and antiquities. Abu Sayyaf may well have had a role in the sale of these resources.

Large cultural artifacts that the militants cannot smuggle and are deemed idolatrous are often destroyed. But smaller items find their way to international black markets.

The Islamic State is estimated to control more than 4,500 ancient archeological sites in Syria and Iraq.

However, some experts have questioned whether all the items handed over to Iraq on Wednesday were genuine.

Donna Yates, an archaeologist who researches artifact smuggling at the University of Glasgow, raised doubts about an item that appeared to be a fake Nefertiti bust. “It would be funny if it wasn’t so sad,” she tweeted.

Iraqi authorities said that they had not had time to properly date and verify the items, and that it was too early to tell whether any of the artifacts recovered were recently excavated from those archeological sites controlled by the Islamic State.

Some, though, had been changing hands in the region for years, they said.

Receipts that were also handed over with the items documented illicit sales dating to the 1980s, suggesting that if they were Abu Sayyaf’s, he may have been in the smuggling game for decades.

Little is known about Abu Sayyaf. U.S. officials have said that he was Tunisian. His Iraqi wife, known as Umm Sayyaf, was captured in the raid and is in U.S. military detention in Iraq.

Among the items found in the house were three Babylonian stone seals, which officials said were stolen in 2003 from the National Museum of Iraq in Baghdad during the chaos that followed the U.S.-led invasion of Iraq. Their museum numbering is still visible.

Exactly how they ended up in Abu Sayyaf’s compound in Syria, no one knows.

“We’re just happy to have them back,” said Ahmed Kamil, director general of museums at the Iraqi Culture Ministry.

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