BAGHDAD (AP) — Nearly 500 artifacts recovered by U.S. Special Forces during a raid in Syria targeting the Islamic State group were put on display Wednesday at the Baghdad National Museum.

Many of the relics, including ancient coins and royal seals used by kings in the ancient Assyrian city of Nimrud, disappeared at different times dating back to the 2003 U.S.-led invasion of Iraq. How they ended up with the Islamic State group, which now holds a third of both Iraq and Syria, remains unclear. Delta Force commandos seized them in May after killing Abu Sayyaf, a man identified by the U.S. as the head of the Islamic State group's oil operations.

"The list of Daesh atrocities and crimes is long, and it includes the theft and smuggling of your heritage and culture," U.S. Ambassador to Iraq Stuart Jones said, using the Arabic acronym for the extremist group. "Daesh is stealing your antiquities, and we are giving them back to you."

Officials did not offer a value for the recovered artifacts. Nor did the Delta Force mission that recovered them get discussed in detail. U.S. media reports have suggested American hostage Kayla Mueller, whose death was announced in February, spent time in the custody of a Tunisian Islamic State finance man known as Abu Sayyaf.

Islamic State extremists have looted and destroyed several ancient sites in Iraq and Syria as part of its campaign to cleanse the territory it controls of items the extremists deem as non-Islamic. Earlier this year, the militant group targeted a number of ancient sites in northern Iraq, including Nimrud and Hatra, two UNESCO World Heritage sites. In May, the group seized the Syrian town of Palmyra, home to a famed Roman amphitheater.