A team of United Nations experts has urged that Machu Picchu, the "Lost City of the Incas," be placed on an endangered list.

The International Council on Monuments and Sites said heavy tourism could damage the nearly 600-year-old stone structure.

The site is located on the highest part of the eastern Andes, 500 kilometres southeast of Lima, Peru.

Francesco Bandarin, the heritage chief of the UN Educational, Scientific and Cultural Organization (UNESCO), criticized the lack of planning near the site. UNESCO oversees heritage sites. Bandarin said the town of Aguas Calientes, at the bottom of the site, is expanding too fast.

Bandarin said he was worried about the 1,000 tourists that arrive every day at the site, which dates back to the mid-15th century. The Peruvian government estimates one million visitors will visit the site in 2004, double the number from the previous year.

Machu Picchu became a UN World Heritage Site in 1983, but this only provides paper protection.

UNESCO officials said once a site is on the endangered list, they "generally benefit from more effective national measures and increased international funding."

The ancient fortress is believed to be a religious sanctuary and remains the most intact Inca site because the Spaniards never found it.

Machu Picchu was rediscovered by an American explorer, Hiram Bingham, in 1911.