Boxes containing pigs' heads have been sent to the Israeli embassy in Rome and the city's synagogue, Italian media reported Saturday.
The package mailed to the embassy in the wealthy Parioli area of the Italian capital was intercepted by police after other similar parcels were sent to the synagogue and the Jewish Museum of Rome.
"Those who insult the Jewish community offend Rome. We reject the intimidation outright," Rome mayor Ignazio Marino said in a tweet.
The synagogue's package was delivered Friday just as staff received an anonymous phone call claiming there was a parcel bomb on site, the reports said.
Bomb disposal experts who rushed to the scene discovered the grisly head, which they believe came from a slaughterhouse.
Police are analyzing fingerprints and DNA traces found on the boxes, which were sealed with packing tape and delivered by the same postal company.
"This is a vile and cowardly act which offends the Jewish community and all Romans on the eve of the memorial day," Nicola Zingaretti, president of Lazio, the region in which the city of Rome is located.
Officials said that anti-Semitic graffiti were also scrawled on the walls of a municipal building in the city.
There was no immediate word on who was behind the acts but police were investigating.
A statement from the American Jewish Committee said the latest acts were "a serious signal of alarm" and it called for increased vigilance and more incisive methods aimed at reinforcing moral and ethical values.
"The consequences of indifference towards such acts, as history teaches us, can lead to a serious degeneration of peaceful coexistence, and of the democratic fabric of society," it said.
The threats come just days ahead of the International Commemoration Day in memory of the victims of the Holocaust on January 27.