By Alvise Armellini

VATICAN CITY (Reuters) -A group of German victims of abuse on Wednesday called on Pope Francis to step up efforts against "sexual and spiritual abuse" by clergy, after completing a 900-km (560 miles) bicycle trek from Munich to the Vatican.

Abuse scandals have shredded the Catholic Church's reputation and have been a major challenge for the pope, who has passed a series of measures aimed at holding the Church hierarchy more accountable, with mixed results.

"Men and women in the service of the Church inflicted severe physical, sexual and psychological violence on people entrusted to their care," the group said in a letter that was handed to Francis during his weekly audience in St Peter's Square.

"We expect you to do everything in your power to ensure that in all corners of the universal Church the issue of sexual and spiritual abuse is seen, dealt with, and prevented through appropriate preventive measures," they added.

The pope stopped to greet the group and chatted with them "for about 20 minutes" one of the victims, Richard Kick, told reporters. "He listened and I think he understood what we wanted to tell him."

Kick, who is 66, was abused as an altar boy between the ages of 8 and 10. He reported it to the church only in 2010, and got an answer seven years later from the Vatican telling him it was too late to go after his abuser, who subsequently died in 2019.

He said Francis told the group to pray for him and promised to pray for them, but "praying is not enough," Kick said. He added the pope said it was "difficult, very difficult" to punish abusers after decades.

The German group, made up of 15 abuse survivors and other supporters, left Munich on May 6 and travelled to Rome with the backing of their local archbishop, Cardinal Reinhard Marx, a former head of the German bishops' conference.

The issue of abuse is particularly sensitive in Germany, where investigations have exposed widespread historical church abuse and cover-up, triggering demands for major changes in the church.

The German bishops' conference is debating a series of reforms in reaction to the abuse crisis, including around issues such as homosexuality, women priests and priestly celibacy, as part of its so-called Synodal Path.

The Vatican has put a brake on such proposals, which are anathema to conservatives and could lead to massive splintering similar to what happened in Anglican and Protestant Churches after they introduced similar changes in recent decades.

(Reporting by Alvise Armellini and Rachel More, editing by Emelia Sithole-Matarise)