Italy’s relationship with J. Paul Getty museum has gone sour following the museum’s appeal of a ruling by the country’s Supreme Court, ordering the return of a prized ancient Greek artwork.

Titled “Statue of a Victorious Youth, 300-100 B.C.”, the life-sized Greek bronze – one of the few of its kind to have survived – was recovered by Italian fishermen off the Adriatic coast in 1964.

Thirteen years later, after changing hands several times, it was purchased by Getty for $4 million, where it has been held since.

The museum on the outskirts of Los Angeles, known for its collection of Greek and Roman antiquities, has returned 40 ancient artefacts to Italy since 2007, under an agreement that allowed for long-term loans of other pieces.

But the contested masterpiece – nicknamed the “Getty Bronze” – was left out of the deal and in 2010 a court order to be seized and returned to Italy, amidst the country’s campaign for repatriation of looted art, marked the beginning of a legal battle.

According to ANSA news agency, the Court of Cassation rejected the museum’s appeal of the ruling earlier this week. But the Getty issued a statement saying the would “continue to defend our legal right to the statue”, maintaining that Italy has no legal or factual claim supporting the return of the statue.

“Accidental discovery by Italian citizens does not make the statute an Italian object,” the Getty said, citing a 1968 Cassation ruling which found no evidence of the statue belonging to Italy.

“Found outside the territory of any modern state, and immersed in the sea for two millennia, the Bronze has only a fleeting and incidental connection with Italy,” the statement concluded.

Italian authorities however argue that previous trials lacked substantial evidence on the statue’s origin, which prosecutors have recently been able to recover.

“The sculptor was Greek, but the statue was culturally and administratively Italian when it sank,” said Silvia Cecchi, the case prosecutor for a 10-year period. While the artist of the bronze is unknown, some credit Lysippos, Alexander the Great’s personal sculptor.

It remains unclear whether Getty will pursue an appeal to a European court or whether the Italian government intends to try to repatriate the artefact.