Pope Benedict XVI has led an outdoor mass in Germany despite shots being fired close to the service.
A man fired an air-gun at a guard at the edge of the security zone about an hour before the service in the eastern city of Erfurt, Vatican and local officials said.
The pope's spokesman, the Reverend Federico Lombardi, said there was "no worry" among the papal entourage about the incident, and the pontiff was not informed about it before the mass, which was attended by 30,000 people.
Police said the alleged shooter had been arrested and that there were no injuries.
The service came after the pope met German victims of paedophile priests in a bid to stem the loss of support for the Catholic Church in the country.
Last night he met two women and three men from parishes across the country, who were among the abused. The Vatican said the pope expressed "deep compassion and regret" at the suffering of those who were abused and assured them that the Catholic Church is seeking "effective measures to protect children".
Victims have accused the pope of being part of a systematic cover-up by the church hierarchy for paedophile priests in his earlier roles as an archbishop in Germany, and later when he headed the Vatican morals office.
Survivors' groups were quick to denounce the pope's meeting with victims as an empty gesture. They maintain the Catholic Church has not done enough to prosecute offending priests and prevent future abuse.
Following the mass in Erfurt, the pontiff departed for the south-western city of Freiburg, the final stop of his four-day visit.