VATICAN CITY (Reuters) - The Vatican on Friday told an ultra-traditionalist Roman Catholic splinter group they must accept non-negotiable doctrinal principles within a month or risk a painful break with Rome that would have "incalculable" consequences.
The ultimatum was issued after a two-hour meeting between Swiss-born Bishop Bernard Fellay, leader of the dissident Society of Saint Pius X (SSPX) and U.S. Cardinal William Levada, head of the Vatican's doctrinal department.
Levada told Fellay the group's response after years of negotiations was still insufficient to overcome doctrinal problems at the root of the split with Rome.
The SSPX, which rejects reforms made at the historic 1962 Second Vatican Council, defied Rome in 1988 by illegally consecrating four bishops, triggering their excommunication by the late Pope John Paul.
In a gesture of reconciliation, Pope Benedict lifted those bans in 2009 and promoted the use of the traditional Latin Mass favored by the SSPX.
But Benedict has refused to grant SSPX bishops the right to reject some of the Council's teachings, such as its historic reconciliation with Judaism and other faiths.
A Vatican statement warned of a possible "Church rupture that would have painful and incalculable consequences" and demanded that the SSPX clarify its position if it wanted to rejoin the Church and heal the rift.
Vatican spokesman Father Federico Lombardi said the group had been given a month to respond.
He indicated this was the last chance for the traditionalists to come back on board, saying the process had already been a very long one.
"I don't know what else can be done," Lombardi said.
Benedict values the SSPX's commitment to Church traditions and wants to avoid their movement creating a permanent schism claiming to be Catholic but outside Vatican control.
He has shown a keen interest in resolving the matter, including making a number of concessions to the traditionalists such as the limited use of the old-style Latin Mass.
Benedict's opening to the traditionalists has met with resistance in many quarters of the Church, particularly because of the group's reluctance to hold dialogues with other religions.
Last year, the Vatican told Catholic bishops around the world they had to allow priests to say the old-style Latin mass for traditionalist Catholics, whether they liked it or not.
Most Catholics regard the old mass as nostalgic, rigid and something that turns the clock back on the reforms of the Second Vatican Council, which many saw as bringing the Church into modern times.
The return of the Latin liturgy has been controversial even in inter-religious relations.
During Good Friday services in the old liturgy, traditionalists still read a prayer in which they pray that Jews will "recognize Jesus Christ as the savior of all men".
Another question to be resolved will be the status of British-born Bishop Richard Williamson, who caused an uproar by denying the Holocaust just before Benedict lifted the excommunication bans on him and the other SSPX bishops in 2009.
Reporting By Philip Pullella; editing by Barry Moody