Police in Italy announced Tuesday the recovery of dozens of looted artifacts, including a first century fresco and ancient Greek pottery.

Officers broke up a theft ring that operated out of Italy and France, with 31 people under investigation, police said.

Italian police worked with local officials in Switzerland, France and Spain to retrieve the looted artifacts, many of which were illegally removed decades ago.

"These are all objects that had been excavated illegally from underground tombs and taken out of the country," Vito Augelli of the Italian police force that co-ordinated the operation, told reporters.

Among the recovered archeological treasures are vases from the Apulia region dating from fourth century B.C., goblets and other pottery imported from ancient Greece by the Etruscans in central Italy, and a fragment of a fresco believed to date to the first century A.D. and reportedly removed from a villa near Pompeii that served as a home to Emperor Nero's second wife, Poppaea Sabina.

During Italy's three-year hunt for those behind the antiquities-trafficking ring, a raid on a house in Milan also uncovered 22 paintings forged to look like the works of Renoir, Picasso, Modigliani, Monet and Degas, police said in a statement.

Italy has been aggressively pursuing antiquities illegally excavated from its territories, including high-profile campaigns seeking the return of artifacts that landed in prestigious collections of U.S. museums and galleries.

In mid-December, officials opened the exhibit Nostoi: Recovered Masterpieces to showcase the fruits of the past few years, with many of the featured antiquities items returned by California's J. Paul Getty Museum.

Last weekend, Rome's Quirinal presidential gallery, which is hosting the exhibit, announced it would extend the show for an additional month because of popular demand. More than 70,000 people have already seen the exhibit, now set to close on March 30.

With files from the Associated Press