The US has returned 25 artefacts that were looted from Italy, including Etruscan vases, 1st-century frescoes and precious books that had made their way into top US museum, university and private collections.

The items were either spontaneously turned over or were seized by police after Italian authorities noticed them in Christie's auction catalogues or gallery listings and tipped them off.

One 17th-century Venetian cannon was seized by Boston border patrol agents as it was being smuggled from Egypt inside construction equipment.

US ambassador John Phillips joined Italy's Carabinieri police to show off the haul, which included Etruscan vases from the Toledo Museum of Art and the Minneapolis Institute of Art, and 17th-century botany books from Johns Hopkins University.

The items also included a manuscript from the 1500s stolen from the Turin archdiocese in 1990 that ended up listed in the University of South Florida's special collections.

"Italy is blessed with a rich cultural legacy and therefore cursed to suffer the pillaging of important cultural artefacts," Mr Phillips said, adding that Interpol estimates the illicit trade in cultural heritage produces more than nine billion dollars (£5.8 billion) in profits each year.