The famed Route 66 in the United States and Iraq's archaeological sites are among the world's most threatened cultural treasures, according to a list published by a leading US-based heritage group.

The World Monuments Fund's 2008 watch list includes 100 sites from around the world deemed at risk from man-made threats such as climate change, conflict, urban development and unchecked tourism.

"Human activity has become the greatest threat of all to the world's cultural heritage," the non-governmental group said in its report.

"But, just as we caused the damage in the first place, we have the power to repair it," the group's president Bonnie Burnham added.

Among the best known sites on the list are Machu Picchu in Peru, which the fund said was at risk from rampant and unmanaged tourism.