Police and demonstrators clashed briefly in Venice on Friday during a protest against the arrival of a mega-yacht owned by the US ambassador to Italy, Texan businessman Tilman Fertitta.
Several hundred protesters shouted slogans hostile to US policies in the Middle East and tried to get close to the yacht, guarded by masked police officers, local media footage showed.
The 117-metre (384-foot) long Boardwalk entered Venice, accompanied by Italian police speedboats and jet-skis.
It was the latest visit in a tour of Italy's coastline organised by the ambassador to celebrate the 250th anniversary of the US declaration of independence.
Opposition deputies have denounced the cost to the taxpayer of the tour, pointing out that each visit requires a deployment of naval, coastguard and police units to ensure security.
