Italian and Swiss officials signed a deal Friday aimed at making it harder for smugglers of archaeological treasures to use Switzerland as a conduit for stolen antiquities.

Under the deal, customs officials of the two countries will have to ensure that importers of antiquities from both Italy and Switzerland have proof of the artifact's origin and of its lawful export from the neighboring country.

A 1939 Italian law makes all antiquities discovered in the country property of the state, making export of objects found after that date illegal. Authorities contend that looted Italian treasures have often made their way to Switzerland, and from there onto the international market, including European and U.S. museums.

In one of the more spectacular cases, a 1995 raid on the Geneva offices of an Italian art dealer, Giacomo Medici, yielded thousands of photographs and pieces of artifacts police say were looted from Italy. He was later sentenced to a 10-year prison term on art trafficking charges.

The case has since led to the criminal prosecution of Marion True, a former J. Paul Getty Museum curator on trial in Rome accused of knowingly purchasing stolen artifacts from Medici and other dealers. True and Robert Hecht, an American art dealer also on trial on the same charges, deny any wrongdoing.

"The art market in Switzerland is an important market," Swiss Interior Minister Pascal Couchepin said after signing the deal in Rome with Culture Minister Francesco Rutelli. "We strongly wish to have an ethical, clean and responsible market."

"Traffickers will have to go somewhere else," Rutelli told reporters, adding that the growing awareness of the illegal trade "is making it increasingly difficult to sell stolen or looted art."

The deal only protects artifacts that date from before the 16th century, and both ministers expressed hope that it will be extended to safeguard art produced from the Renaissance onwards.