Peru says it will take legal action to recover thousands of artefacts from the Inca citadel of Machu Picchu which are held by Yale University in the US.
Machu Picchu was rediscovered by a Yale graduate in 1911
The artefacts were taken to Yale by former student Hiram Bingham, the first modern explorer to reach the citadel.
Peru says it agreed to their removal on condition that they would be returned.
But Yale says it followed standard collecting practices at the time, and that it has made a reasonable offer to return some of the artefacts.
The Peruvian government announced it would take its case before a US court after three years of talks ended without agreement.
Peru's ambassador to Washington, Eduardo Ferrero, said Yale had "refused to acknowledge Peru's ownership of the artefacts".
"[Yale] proposes that these artefacts belong to humanity, and at the same time pretends to keep part of the collection," he said.
The US university said it had proposed to work with the Peruvian government to set up parallel exhibitions of Inca objects at Yale and at a new museum to be built in Peru.
Peru wants the objects back in time for a big exhibition it is planning to mark the centenary of Bingham's expedition.
In 1911, Bingham rediscovered Machu Picchu which had lain forgotten for hundreds of years.
His team dug up nearly 5,000 artefacts at the site, including ceramics and jewellery.