European rabbis urged the Vatican on Wednesday to suspend unity talks with an ultra-traditionalist Catholic rebel society until the movement pledged to fight what they called anti-Semitism in its ranks.

The Conference of European Rabbis said Bishop Richard Williamson – already known for publicly denying the Holocaust – and the head of the splinter group in France had recently revived the age-old accusation that Jews killed Jesus.

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The statement came as the dissident Society of Saint Pius X (SSPX) considered a final offer from the Vatican to end their 23-year split and reintegrate the rebels who firmly reject modernizing reforms the Catholic Church made in the 1960s.

Both Williamson and French SSPX head Rev Regis de Cacqueray, two outspoken critics of any compromise with the Vatican, recently repeated the charge against the Jews, as Pope Benedict prepared to host world faith leaders – including Jews – in Assisi, Italy next week.

"There must be no rapprochement within the Catholic Church for those of its flock who seek to preach words of hate," said Conference head Rabbi Pinchas Goldschmidt in a statement.

"We call upon the Catholic Church to suspend negotiations with extremist Catholic tendencies until it is clear that these groups show a clear commitment to tackling anti-Semitism within their ranks," said Goldschmidt, whose Brussels-based group represents chief rabbis and senior rabbinical judges across Europe.

The Roman Catholic Church said at the Second Vatican Council (1962-1965) that it did not hold the Jews responsible for the killing of Christ, launching an era of improved relations between Catholics and Jews.

But issues concerning the Holocaust, including Williamson's denial and Benedict's support for the beatification of wartime Pope Pius XII, despite statements by some historians and Jewish leaders that he did not do enough to support persecuted Jews, still cause friction.

After two years of discussions with the SSPX, the Vatican said last month the movement would have to agree to a list of fundamental Church teachings if its four bishops were to be reintegrated in to the Church. The list was not made public.

The four, including Williamson, were excommunicated in 1988 when they were ordained by SSPX founder Archbishop Marcel Lefebvre against orders from the Vatican.

Williamson, who lives in Britain, was conspicuously absent from a recent meeting of SSPX leaders near Rome to consider the Vatican demand. Remarks by SSPX leader Bishop Bernard Fellay since then hinted the group could not agree with the Vatican.

The SSPX is expected to deliver its response to the Vatican within a few months.