VATICAN CITY - Pope Francis on Thursday overturned centuries of tradition that banned women from a foot-washing service during Lent, upsetting conservatives and delighting women's rights activists.

Until now, only men or boys were formally allowed to take part in the service, in which a priest washes and kisses the feet of 12 people to commemorate Jesus' gesture of humility towards his apostles on the night before he died.

But in a letter to the Vatican department that regulates rites of worship, Francis said the group should be made up of "all members of the people of God," including women.

The ritual takes place in Catholic parishes around the world the world on Holy Thursday, four days before Easter. While some parishes in the 1.2 billion member Church had already included women and girls, most have stuck to the written rules, particularly in developing countries.

"This is great news, a wonderful step forward," said Erin Hanna, co-director of the US-based Woman's Ordination Conference, which promotes a female Catholic priesthood.

"This means that change is possible, doors seem to be opening in the Vatican," she told Reuters.

Since his election in 2013, the pope has included women when he has presided at the foot-washing services, continuing a practice he started when he was archbishop of Buenos Aires.

He has held these services in a home for the elderly and even included Muslims when he held them in Italian jails, outraging traditionalists.

"I feel very sorry for priests who have been trying to obey liturgical law on this issue ... they may well feel betrayed," Joseph Shaw, head of a traditionalist group called The Latin Mass Society, said of the new rules.

"Liturgical conservatives who have sought in recent decades to keep the rules ... often in the face of considerable pressure, may well feel the rug has been pulled from under them by this decree," he said in a statement.

A decree issued on the pope's behalf by Cardinal Robert Sarah of Guinea said Jesus had "given his life for the salvation of all of humanity" and the group should be a mix of men, women, old people, young people, the sick and the healthy.

The pope has said he wants to put women in more positions of power in the Vatican and the Church worldwide, but he has ruled out allowing women priests, saying "the door is closed" on the issue. — Reuters