The Swiss-born founder of the Taizé ecumenical community, Brother Roger, has died after being attacked during a religious service.
Police said a woman stabbed the 90-year-old cleric three times in the throat during the service at the Taizé community in eastern France. He died immediately.
A 36-year-old Romanian woman was overpowered by worshippers and detained.
Around 2,500 mainly young people were attending the service when the attack happened.
Brother Roger was one of the leading ecumenical figures of the 20th century.
A Protestant pastor from western Switzerland, he enjoyed great respect among religious leaders and Pope John Paul II visited his monastic community.
A spokesman for the Taizé community said the woman approached Brother Roger during the service but was not noticed because the brothers had their backs to her. "We heard a cry, turned around and it was already done."
Pope Benedict said on Wednesday that he was shocked by the "terrifying" murder of Brother Roger.
The bishop of Lausanne, Geneva and Fribourg, Monsigneur Bernard Genoud, condemned the killing, which happened on Tuesday night. He has sent his condolences and prayers to the Taizé community.
The Council of the Federation of Swiss Protestant Churches said in a statement it was "shocked" to learn of the violent death of the Taizé founder.
"Entire generations of Swiss pastors and lay people active in the church were influenced by Brother Roger," it said. "He increased the standing of the monastic community within Protestantism and gave vital impetus to ecumenism."
Organisers of the Roman Catholic Church's World Youth Day event in the German city of Cologne expressed dismay at the killing.
"Brother Roger has always been closely attached to the Catholic Church," Heiner Koch, the secretary general of the event, said in a statement.
The elderly cleric founded the Taizé monastic community in 1940 after leaving Switzerland at the age of 25 and buying a small house in the village.
Today the Taizé community is made up of over 100 brothers, including Catholics and Protestants, from more than 25 nations.
A German Taizé brother will succeed Brother Roger as head of the community. Brother Alois (51) left Cologne, where he was attending World Youth Day, to return to Taizé.
Brother Roger designated the German Catholic as his successor eight years ago, a spokesman said. Brother Alois has been with the community for 32 years.
swissinfo with agencies
Protestant pastor Roger Schutz-Marsauche founded the Taizé community in 1940.
In 1945 the first brothers, all Protestant, arrived from Switzerland.
Today the community is made up of more than 100 brothers from different Christian faiths and more than 25 different countries.
Up to 100,000 people, especially young people, visit Taizé every year for a weekend or week of reflection and prayer.
Taizé songs and prayers are used in churches all over the world.
Numerous dignitaries have visited the community near Dijon in France: Former Czech President Vaclav Havel, Nelson Mandela, Mother Teresa, Pope John Paul II.