A Bar-Ilan University historian has raised a storm by alleging in a new book that some blood libels - accusations that Jews killed Christians in ritual murders to add their blood to matza and wine on Passover - may be based on real ceremonies in which the blood of Christians was actually used.

"Pasque di Sangue," by Ariel Toaff, was just released in Italy. It shocked the country's small Jewish community - in part because he is the son of Elio Toaff, the chief rabbi who welcomed Pope John Paul II to Rome's synagogue two decades ago in a historic visit that helped ease Catholic-Jewish relations after centuries of tensions.

The author, who is considered an international expert on Italian Jewry, delves into allegations that resulted in torture, show trials and executions, periodically devastating Europe's Jewish communities.

Historians have long dismissed the allegations as racism, but blood libel stories remain popular in anti-Semitic literature.

Jewish and Catholic scholars have denounced Toaff's work, saying he simply reinterpreted known documents - and has given credence to confessions extracted under torture.

In an interview with the Italian newspaper La Stampa, Toaff responded angrily to his critics, saying, "My research shows that in the Middle Ages, a group of fundamentalist Jews did not respect the biblical prohibition and used blood for healing. It is just one group of Jews, who belonged to the communities that suffered the severest persecution during the Crusades. From this trauma came a passion for revenge that in some cases led to responses, among them ritual murder of Christian children."

Italian rabbis issued a statement recalling that Jewish law has always banned ingesting blood or using it for rituals.

Toaff's 91-year-old father said he was looking forward to reading his son's book and examining the documents, but stressed that according to the Torah and tradition, the consumption of animal blood was strictly prohibited, not to mention that of humans.

In an interview Friday with The Associated Press, Toaff said, "There is no proof that Jews committed such an act." But he added that the confessions do hold some truth - as when the accused recount anti-Christian liturgies that were mainly used on Passover, when the Israelites' liberation from ancient Egypt became a metaphor for Judaism's hope for redemption from its suffering at the hands of Christians.

"These liturgical formulas in Hebrew cannot be projections of the judges who could not know these prayers, which didn't belong to Italian rites but to the Ashkenazi tradition," he said.

The 65-year-old Toaff, a rabbi who holds dual Italian and Israeli citizenship, said, "I wanted to see how the Jews felt in this climate of hatred."

Monsignor Iginio Rogger, a church historian who in the 1960s led the investigation into the murder of a 2-year-old Simon of Trento, for which 16 Jews were hanged, said many scholars have concurred that the confessions were completely unreliable.

"I wouldn't want to be in [Toaff's] shoes, answering for this to historians who have seriously documented this case," he said. "The judges used horrible tortures, to the point where the accused pleaded: 'Tell us what you want us to say.'"

Hebrew University historian Professor Israel J. Yuval, a blood-libel expert, said, "From the information I have received, Professor Toaff's interpretation sounds trumped-up."

The Anti-Defamation League chairman, Abe Foxman, said, "It's hard for me to believe that someone, especially an Israeli historian, would legitimize the baseless claims of the blood libels."

Bar-Ilan University spokesman, Shmulik Algrabli, said, "Professor Toaff is one of the greatest scholars in his field, and we have confidence in his scientific method. The contentions of the study will be clarified when the author returns to Israel."