By Saif Hameed

BAGHDAD (Reuters) - The United States handed back to Iraq on Wednesday antiquities it said it had seized in a raid on Islamic State fighters in Syria, saying the haul was proof the militants were funding their war by smuggling ancient treasures.

The Iraqi relics were captured by U.S. special forces in an operation in May against an Islamic State commander known as Abu Sayyaf. They included ancient cylindrical stamps, pottery, metallic bracelets and other jewelry, and glass shards from what appeared to be a colored vase.

The haul also included early Islamic coins.

Islamic State, a hardline Sunni Islamist group, has ransacked some of the greatest archaeological sites in northern Iraq, posting video footage of fighters destroying pre-Islamic monuments they consider idolatrous.

Iraqi officials have been unable to verify the full extent of damage at the sites under Islamic State control, but they have said that footage of the destruction was published in part to distract attention from the fact Islamic State is smuggling antiquities to raise cash.

"This is the first tangible evidence that Daesh are selling artefacts to fund their activities," U.S. ambassador Stuart Jones, said, referring to Islamic State by its Arabic acronym.

"Their goal is to sell these antiquities on the global black market," he told reporters at Baghdad's national museum where the items were handed over.

Abu Sayyaf, who was killed in the raid, was described by U.S. officials at the time as an Islamic State commander responsible for the group's oil and gas sales.

He was killed south-east of the city of Deir al-Zor, near Syria's main oil fields and about 100 km (60 miles) from the Syria-Iraqi border across which Islamic State declared its "caliphate".

"Today’s effort represents one success in the efforts to return Iraq’s historic patrimony, but the campaign to return all of Iraq’s treasures continues," Jones said.

Islamic State fighters have desecrated ancient Assyrian and Graeco-Roman palaces in northern Iraq including the 2,700-year-old Assyrian capital of Khorsabad, the cities of Nimrud and Nineveh and the desert complex at Hatra.

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Iraqi officials have appealed for international help to protect the sites, asking why the U.S.-led coalition which has been bombing Islamic State bases and convoys across Iraq and Syria has not deployed its air power in defending the ancient treasures.

Jones said that, in the absence of forces on the ground, aerial bombardment near the remains would have limited effect and could be self-defeating.

"The coalition does not have boots on the ground and certainly using air strikes on targets like that can be damaging to the patrimony of Iraq," he said.

(Writing by Dominic Evans; Editing by Robin Pomeroy)