The Vatican will tell a rebel traditionalist group it must respect Judaism, other Christian churches and other world faiths to be fully reintegrated into the Roman Catholic Church, a leading cardinal has said.

Vienna Cardinal Christoph Schoenborn said these reforms of the Second Vatican Council, which the traditionalist Society of St Pius X (SSPX) rejects, were "not negotiable" in doctrinal discussions due to start soon between the Vatican and the group.

"It's not the case that Rome will let the Lefebvrists off easy for everything," Cardinal Schoenborn told the German daily Passauer Neue Presse, calling the traditionalists after their founder Archbishop Marcel Lefebvre, who broke with Rome in 1988.

Pope Benedict triggered a controversy in the Church and with Jewish leaders in January by lifting the excommunication of the SSPX's four bishops, including one who denied the Holocaust. He later said the Vatican handled the case badly.

The SSPX broke with Rome in a dispute over the 1962-1965 Council, especially its call for respect for other faiths. The Vatican said it would have to discuss this teaching before its priests could exercise any ministry in the Church.

"The negotiations between a newly appointed Vatican commission and the SSPX will begin in the next few days," Cardinal Schoenborn, a close associate of Pope Benedict, told the newspaper published in the Pope's native Bavaria.

"The SSPX will be told very clearly what is not negotiable for the Holy See," he said. "This includes such fundamental conclusions of the Second Vatican Council as its positions on Judaism, other non-Christian religions, other Christian churches and on religious freedom as a basic human right."

The lifting of the excommunication of British-born Bishop Richard Williamson, who denied the Nazis killed Jews in gas chambers, prompted world Jewish leaders to tell the Vatican that Holocaust denial was "not an opinion but a crime".

Pope Benedict has made several concessions to the SSPX, including wider use of the traditional Latin Mass the group champions, to bring its 500 or so priests back into the Roman fold. Critics charge he has betrayed the Council reforms to win them back.

Catholic prelates in German-speaking countries, including Scho-enborn, have been outspoken in demanding the SSPX must explicitly accept the Council's opening to the Jews.

Since the excommunications were lifted, SSPX head Bishop Bernard Fellay has hinted at possible minimal changes in the group's interpretation of the Council, but other bishops have maintained the group's traditional rejection of its reforms.