Allen said the 2003 war bought the restoration project some time because it prevented premature, ill-supervised development of the site. But looters rampaged through Babylon after the U.S.-led invasion, and U.S. forces stuffed sandbags with dirt that contained ancient pottery and brick fragments, the UNESCO assessment said.

It said U.S. forces and the contractors they employed, mainly KBR, then a Halliburton subsidiary, "caused major damage to the city by digging, cutting, scraping, and leveling."

The U.S. military did not immediately respond to requests for comment, but in the past it has said looting would have been worse had its troops not been there.

The report said steel stakes were driven into ancient walls, which included fragments with inscriptions from the time of King Nebuchadnezzar II, who ruled 2 1/2 millennia ago and is credited with building the Hanging Gardens of Babylon - one of the Seven Wonders of the World.

A helicopter pad, roads and parking lots were bu