Greece has struck a deal for the eventual return from a US billionaire’s private collection of 161 ancient Greek artifacts dating from more than 4,500 years ago.

Greek Government spokesman Yannis Oikonomou said last Tuesday that Greece’s Parliament will vote on draft legislation to ratify the agreement, which involves New York’s Metropolitan Museum of Art, (MET), a top Greek museum, and a Delaware-based cultural institute.

Oikonomou said the agreement, which avoids any legal dispute or payment by the Greek government, could serve as a model for further restitutions. It’s expected to be tabled in Parliament early next week.

“This creates a procedure and a means that encourages other collectors of Greek antiquities to make similar moves… that don’t carry the disadvantages of a court process,” he said.

The main opposition socialist party SYRIZA is against the deal saying that it legitimates theft of Greece’s cultural heritage. SYRIZA called for the withdrawal of the bill, saying it “smooths the ground for the legalization of antiquities theft and illegal exports of antiquities.”

The government spokesperson, Mr Oikonomou said the deal recognised Greece’s ownership of the artifacts from the Early Bronze Age Cycladic civilization — known for its abstract but enigmatic marble figurines — donated by a New York collector to the Delaware institute.

The works will first be exhibited later this year at the Museum of Cycladic Art in Athens, and subsequently at the Metropolitan Museum, he said.

Antiquities of indeterminate provenance are usually plundered and devoid of any information on their function and cultural significance that a legitimate excavation would have provided. Mr Oikonomou provided no details on how the works had been excavated and exported from Greece and described them as “unknown” artifacts.

The MET declined to comment.

Mr Oikonomou did not name the U.S. collector involved. But two people with knowledge of the agreement told The Associated Press that the artifacts were from the collection of Leonard. N. Stern, an 84-year-old pet supplies and real estate businessman and philanthropist. They spoke on condition of anonymity pending official announcements.

“Many of (the pieces) are extremely rare or even unique examples of the art and artisanship of the 3rd millennium BC Cycladic civilization and offer new data to scientific knowledge of the period,” Mr Oikonomou said in a statement after a Cabinet meeting discussed the deal Tuesday.

A Greek official said the 161 antiquities would be gradually returned to Greece for permanent display, but no precise time frame was available.

The Cycladic civilization flourished in the Cyclades Island group of the Aegean Sea roughly between 3800-2000 BC. It’s best known for the iconic white marble figurines of naked female forms that inspired artists including Pablo Picasso and Constantin Brancusi. Their huge popularity among private collectors and museums worldwide sparked an orgy of illegal excavations across the Cyclades in the 20th century. Largely due to that, their precise original function remains unclear.

For decades, Greek authorities have strived to recoup antiquities illegally excavated and exported from the country, which can be sold for millions of dollars.

Athens has long and fruitlessly lobbied to get back large sections of the 5th century BC sculptures that originally decorated the Parthenon Temple on the Acropolis and are now in the British Museum in London.