Pope Francis on Friday branded anti-Semitism part of a wave of "depraved hatred" sweeping some countries and urged everyone to be vigilant against it.

In comments to members of the American Jewish Committee during a visit to the Vatican, he also reiterated that it was sinful for Christians to hold anti-Semitic sentiments because they shared a heritage with Jews.

"A source of great concern to me is the spread, in many places, of a climate of wickedness and fury, in which an excessive and depraved hatred is taking root," Francis said.

"I think especially of the outbreak of anti-Semitic attacks in various countries."

Francis did not name any of those countries, but government statistics released last month showed more than 500 anti-Semitic attacks occurred last year in France, which has Europe's biggest Jewish community.

That was a 74 percent increase from 2017.

"I stress that for a Christian any form of anti-Semitism is a rejection of one's own origins, a complete contradiction," Francis said.

A European Union study last month showed that more than one in three European Jews have considered emigrating in the past five years because they no longer feel safe.

Episodes of anti-Semitism have coincided with the rise of populist or nationalist parties in predominantly Christian countries such as Italy, Germany, Poland and Hungary.

In Britain, nine lawmakers quit the Labour party last month, citing the leadership's handling of anti-Semitism in the party as a reason for leaving.

In December, 20 cobblestones commemorating members of two Italian Jewish families who were deported to Auschwitz or killed in Rome were dug up and stolen in what the Jewish community said was an anti-Semitic attack.

On Monday, Pope Francis announced that he has decided to open fully the Vatican's secret archives on Pope Pius XII, something which Jews have been seeking for decades.

Some Jews have accused Pius, who reigned from 1939 to 1958, of turning a blind eye to the Holocaust during World War Two by not speaking out forcefully. The Vatican has said Pius worked quietly behind the scenes to save Jews and avoid worsening the situation for many.