BERLIN — The German police said Saturday that they had arrested a man suspected of shooting a security guard with an air gun in the eastern city of Erfurt shortly before Pope Benedict XVI was about to celebrate Mass.

But a Vatican spokesman, the Rev. Federico Lombardi, said there was “no worry” for the papal entourage. The episode occurred close to the zone established to protect the pope and carry out security checks on the pilgrims.

Thousands of pilgrims had already lined up during the early hours of the cold morning to get as close as possible to the pope.

A local police spokesman said the man was arrested in his apartment in Erfurt, from where the shots were fired, Agence France-Presse reported. The shots were fired about two hours before Benedict, 84, began celebrating Mass before 30,000 people. No one was injured.

The pope was beginning the third day of his four-day official visit to Germany, where security has been extremely tight. He had already faced large protests in Berlin on Thursday, where the German-born pope addressed the Bundestag, or parliament.

On Friday, the pope reached out to other faiths, meeting Muslims in Berlin and later the leadership of the Protestant Church in Erfurt. It was in Erfurt where Martin Luther studied before he initiated the Protestant Reform that led to a split from the Catholic Church nearly 500 years ago.