Peruvian president Alan Garcia has asked Yale University to return the archaeological treasuries its researchers "looted" from the country's Machu Picchu site in the early 1900s.
Peru says Yale took some 40,000 of artefacts including pottery, jewellery and bones from the site in the Peruvian Andes.
"Either we come to an understanding regarding . . . Machu Picchu, or we'll simply have to describe them as looters of treasuries," Mr Garcia said referring to Yale University.
The artefacts were sent out of Peru after a Yale alumnus, US explorer Hiram Bingham, rediscovered Machu Picchu in 1911.
The Andean country argues the objects were loaned to Yale for 18 months but never sent back.
"Now is the time to start packing up the things and send then over together with the research. ... Silence would indicate that they are guilty of robbery," Mr Garcia said.
At the time of Bingham's find, the ancient city, now a tourist hot spot, was essentially forgotten, covered by thick forest in the mountains some 8,000 feet (2,400 metres) above sea level.
Peru is dotted with hundreds of archaeological sites and has struggled for years to combat trafficking of fossils and artefacts.
Reuters