The ancient tablet, which a wealthy US collector had acquired along with other Iraqi artifacts to display in the Washington Museum of the Bible, will be handed over to Iraqi officials at the Smithsonian Institution on September 23.

UNESCO called the repatriation of the tablet, along with 17,000 other artifacts sent back to Iraq in July, "a significant victory in the fight against the illicit trafficking of cultural objects."

"The theft and illicit trafficking of ancient artefacts continues to be a key funding source for terrorist groups and other organised criminal organisations," the Paris-based agency said in a statement.

It said that when the Islamic State extremist group controlled large parts of Iraq and Syria over 2014-2019, Iraqi archaeological sites and museums were systematically looted.

The rare fragment, which recounts a dream sequence from the Gilgamesh epic in Akkadian cuneiform script, is one of many ancient artifacts from Iraq and the Middle East collected by David Green, the billionaire owner of the Hobby Lobby craft store chain.

It was seized by the US Justice Department in 2019, two years after Green opened the museum dedicated to ancient Christian history in downtown Washington.