State newspaper, El Peruano said Sunday the Justice Ministry will assign a prosecutor to press the government's case against the New Haven university. It did not say when or where such a suit would be filed. Government officials could not immediately be reached to confirm the information.
Thomas Conroy, a Yale spokesman, said the university was aware of the news report.
"It is, of course, disappointing, since we had a positive informal meeting with the foreign minister, and have expected to have further discussions," he said. Yale has stated in the past that it will defend any lawsuit.
"We believe that a lawsuit does not best serve the interests of the public, both in Peru and internationally, or of posterity," Conroy said.
The university, Conroy added, continues to believe that "cooperation and collaboration would provide a better framework for satisfying the multiple interests in the archaeological material excavated by Hiram Bingham III at Machu Picchu."
Peru demanded the collection back in 2006, saying it had never relinquished ownership when Bingham, a Yale scholar, rediscovered Machu Picchu in 1911 and sent thousands of ceramics, textiles and bones to the university.
Peruvian officials have threatened to sue in the past but never did.
Peru and Yale reached an agreement in 2008, but it fell through over a dispute over how many artifacts were to be returned.
The mountaintop Machu Picchu ruins are Peru's main tourist attraction.