VATICAN CITY (Reuters) - Pope Benedict rehabilitated on Saturday a traditionalist bishop who denies the Holocaust, despite warnings from Jewish leaders that it would seriously harm Catholic-Jewish relations and foment anti-Semitism.

The Vatican said the pope issued a decree lifting the excommunication of four traditionalist bishops who were thrown out of the Roman Catholic Church in 1988 for being ordained without Vatican permission.

The four bishops lead the ultra-conservative Society of Saint Pius X (SSPX), which has about 600,000 members and rejected modernizations of Roman Catholic worship and doctrine.

The Vatican said the excommunications were lifted after the bishops affirmed their willingness to accept Church teachings and papal authority.

In healing a 20-year-old schism that had wounded the Catholic Church, the decree looks set to spark one of the most serious crises in Catholic-Jewish relations in 50 years.

“We have no intention of interfering in the internal workings of the Catholic Church, however, the eagerness to bring a Holocaust denier back into the Church will cast a shadow on relations between Jews and the Catholic Church,” Israel’s ambassador to the Vatican Mordechai Lewy, told Reuters.

One of the four bishops, the British-born Richard Williamson, has made a number of statements denying the full extent of the Nazi Holocaust of European Jews, as accepted by mainstream historians.

In comments to Swedish television broadcast on Wednesday, he said “I believe there were no gas chambers” and only up to 300,000 Jews perished in Nazi concentration camps, instead of 6 million.

Williamson said: “I believe that the historical evidence is hugely against 6 million having been deliberately gassed in gas chambers as a deliberate policy of Adolf Hitler.”

Pope Benedict XVI waves at the end of his Wednesday general audience in the Paul VI hall at the Vatican in this recent photo from January 21, 2009. REUTERS/Tony Gentile

Israel-based Rabbi David Rosen, head of inter-religious affairs for the American Jewish Committee, told Reuters:.

“The late Pope John Paul II called anti-Semitism a sin against God and man. The denial of the overwhelmingly detailed documentation of the Shoah is anti-Semitism at its most blatant.

“In welcoming an open Holocaust denier into the Catholic Church without any recantation on his part, the Vatican has made a mockery of John Paul II’s moving and impressive repudiation and condemnation of anti-Semitism,” he said.

VATICAN DEFENDS DECREE

Asked about Williamson’s comments, chief Vatican spokesman Father Federico Lombardi said they were “totally extraneous” to the lifting of the excommunications.

“This act regards the lifting of the excommunications, period,” Lombardi told reporters.

“It has nothing to do with the personal opinions of a person, which are open to criticism, but are not pertinent to this decree.”

Elan Steinberg, vice president of the American Gathering of Holocaust Survivors and their Descendants, told Reuters: “At a time when the Vatican should have sided with the victims it acted instead to desecrate their memory.

“This was an act of moral debasement unworthy of a moral institution. For this Vatican political expediency trumps ethical and human considerations,” he said.

Catholic-Jewish relations were already severely strained over the figure of wartime Pope Pius XII, who Jews have accused of turning a blind eye to the Holocaust. Jews have asked the Vatican, which denies the charges, to freeze the procedure that can lead to his sainthood pending more study of wartime records.

Pope Benedict has already made several gestures of reconciliation to the schismatic group, including allowing the unconditional return of the old-style Latin Mass.

That move also angered Jews because the ceremony includes a Good Friday prayer for their conversion.