Erfurt, Germany: A shooting incident one kilometer (600 yards) from where Pope Benedict XVI was celebrating mass Saturday had no link with the pontiff, a Vatican spokesman said.

A man fired four shots from an air gun in the German city of Erfurt, police said, but Vatican spokesman Federico Lombardi said it was "an incident that had nothing to do with the pope" and that "the pope has not been informed."

"No one noticed," Lombardi added. The shots were fired around two hours before Benedict began his celebration of the mass for around 30,000 people.

"According to the German police, it seems to be the action of an unbalanced person," said Lombardi.

Dirk Sauter, a spokesman from the state police in Thueringen, said: "Between 7:00 am (0500 GMT) and 8:00 am, a total of four shots were fired at two members of a security firm."

"Neither person was hurt ... a suspect was taken into custody in an apartment. It was not the tenant of this apartment. An investigation has been launched against this person for attempted grievous bodily harm," said Sauter.

"Two air guns were secured," he added.

Security for the pope's first state visit to his native Germany has been extremely tight. Large parts of Berlin, Erfurt and Freiburg have been locked down for the trip amid a colossal police presence.

But a police spokesman in Freiburg, the pope's next stop on his four-day trip, said there were no specific plans to boost police presence in the city as a result.

Chief inspector Uwe Vincon told AFP: "We are not going to let ourselves be scared by this." The incident in Erfurt had "no political motive," he said.

By the time the man was arrested, the pope was already at the airport on his way to the staunchly Catholic city of Freiburg in southwestern Germany, where he was due to hold a prayer vigil for young people later Saturday.

Addressing the cheering, flag-waving crowd of around 30,000 in Erfurt, in former East Germany, Benedict paid tribute to those Catholics who had kept the faith burning during Nazi and Communist regimes.

"You have had to endure first a brown and then a red dictatorship, which acted on the Christian faith like acid rain," he told worshippers. Erfurt was home to one of the most resilient Catholic communities under communism.

On the first two days of his visit, Benedict met members of Germany's Jewish and Muslim communities and then held prayers with Protestant leaders in a show of greater Christian unity.