By Tom Heneghan, Religion Editor
PARIS (Reuters) - A rebel Catholic group at the heart of major controversies that plagued former Pope Benedict has begun criticising his successor Pope Francis for the popular approach he has taken since his election last month.
In a letter to supporters this week, the head of the ultra- traditionalist Society of Saint Pius X (SSPX) asked whether the new pontiff's focus on serving people could be only "man-centred philanthropy" rather than true religious leadership.
Bishop Bernard Fellay's sharp criticisms of the Vatican attracted attention during Benedict's papacy because the now retired head of the Roman Catholic Church wanted to reintegrate the once-excommunicated group fully into the Roman fold.
Francis, the former Argentine Cardinal Jorge Bergoglio, has upset many Catholic traditionalists by eschewing Vatican pomp, presenting himself as a humble servant of the poor and showing little interest in returning to centuries-old traditions.
In his letter, Fellay urged Francis "not to allow souls to perish because they no longer learn sound doctrine", by which he meant the ultra-traditionalist views the SSPX advocates.
"What good is it to devote oneself to serving people if it hides from them what is essential?" asked Fellay, whose group claims 500 priests and a million followers around the world.
Aiding the poor has always been a concern for the Church, he said, "but if it becomes merely man-centred philanthropy, then the Church is no longer carrying out its mission".
Fellay, who had long hoped that Benedict would give in and reintegrate his group without conditions, had avoided public comment on his successor until now.
Soon after his election, the SSPX head for South America, Rev Christian Bouchacourt, denounced Francis's simple style as humiliating and undignified for the Church.
"NOT A CATHOLIC"
While Benedict criticised some reforms of the 1962-1965 Second Vatican Council, Francis praised it on Tuesday as "a beautiful work of the Holy Spirit" that remained to be fully implemented although some wanted to turn back the clock.
Benedict's wooing of the SSPX, part of a his wider plan to bring back many Catholic traditions sidelined after Vatican II, triggered several controversies during his eight-year papacy.
His 2007 decision to allow wider use of the old Latin Mass met with a mixed reaction among Catholics and Jewish groups said it revived an old Latin prayer they considered anti-Semitic.
Two years later, Benedict set off a firestorm of criticism from Catholics, Jews and German politicians when he lifted the excommunications on the four SSPX bishops, including the notorious Holocaust-denier Bishop Richard Williamson.
Lifting the excommunications meant the four bishops were once again full members of the 1.2-billion member Church, but they and the SSPX had no official position or role within it.
In 2010, the Vatican launched theological discussions with the rebels aimed at an agreement that would make the SSPX a "personal prelature" or autonomous institution in the Church.
They ended in deadlock last year and Benedict made clear he would not give in on central Vatican II reforms such as its opening to dialogue with other faiths, especially Judaism.
Archbishop Gerhard Mueller, the top doctrinal official in Rome, told Germany's Catholic news agency KNA last month that all priests accept the Council's reforms as valid.
"Whoever does not recognise this is not a Catholic," he declared.
(Reporting By Tom Heneghan; Editing by Michael Roddy)