By Philip Pullella
VATICAN CITY (Reuters) - Risking the ire of Catholic traditionalists, Pope Francis is to take part in a joint Catholic-Lutheran service in Sweden in October marking the start of the 500th anniversary of Martin Luther's anti-Catholic Reformation.
The service will take place in the southern Swedish city of Lund on Oct. 31, the Vatican said. Lund is where the Lutheran World Federation was founded in 1947.
Luther, a German, is credited with starting the Protestant Reformation in 1517 with writing 95 theses - famously said to have been nailed to a church door in Wittenberg - criticizing the Catholic Church for selling forgiveness from sins for money.
It led to a violent, often political schism throughout Europe and Christianity, prompting among other things the 30 Years' War, the destruction of English monasteries, and the burning of numerous "heretics" on both sides.
Catholic traditionalists have already accused Francis of making too many concessions to Lutherans, particularly in a "common prayer" that both religions will use during the 2017 commemorations.
They say the prayer excessively praises Luther, who was condemned as a heretic and excommunicated.
Francis, however, has made dialogue with other religions one of the hallmarks of his papacy and the announcement was timed to coincide with the end of the yearly Week of Prayer for Christian Unity.
He has already visited the Lutheran church of Rome, the Waldensian protestant community in northern Italy, and Rome's synagogue. This year he is due to become the first pope to visit the Italian capital's mosque.
While his predecessors have visited protestant churches, Francis has come under criticism from traditionalists who accuse him of sending confusing signals about inter-faith relations.
When he visited Rome's Lutheran church in November he said Catholics and Lutherans should seek forgiveness from each other for "the scandal of division."
They have also contested guidelines issued this month for the "common prayer".
"The Reformation and Martin Luther are repeatedly extolled, while the Counter-Reformation and the Popes and Saints of the 16th century are passed over in total silence," the traditionalist blog Rorate Caeli said.
Theological dialogue between Roman Catholic and Lutherans began in the late 1960s after the Second Vatican Council. But Catholics and Lutherans are still officially not allowed to take communion at each other's services.
When he visited Rome's Lutheran church last year, traditionalists attacked Francis for suggesting in answer to a question that a Lutheran woman married to a Catholic man could decide for herself if she could take communion in her husband's church.
(Additional reporting by Alistair Scrutton Editing by Jeremy Gaunt)