The man, identified as 26-year-old Ibrahim Ak, fired four shots in the air outside the residence of the Italian counsel in the downtown Beyoglu district, shouting "Down with the pope" and "The pope should not come to Turkey," the sources said.
He then threw his pistol into the garden of the building.
As the police took the man to a nearby hospital for a medical check-up, required under detention procedures, he shouted: "I will shoot in the head of those who call the prophet a terrorist."
Benedict XVI is scheduled to pay a four-day visit to Turkey, his first official trip to a Muslim country, starting on November 28.
The visit follows uproar across the Muslim world over remarks by the pope in September linking Islam and violence.
Benedict's comments also provoked fury in Turkey, which slammed the comments as a blow to efforts to reconcile religions. But both the Vatican and Ankara have ruled out cancelling his trip to Turkey.
The visit has raised some security concerns, coupled also with several attacks in Turkey targeting priests.
A Roman Catholic priest was shot dead by a Turkish teenager in the northern city of Trabzon in February at a time when the Muslim world was in uproar over blasphemous sketches of the Prophet Muhammad (SAW) published in European newspapers.
Five days later, another Roman Catholic priest was harassed in western Turkey and in July a third was stabbed by a man described as "mentally disturbed" in the country's north.
Among Turks, Benedict XVI has already won himself a reputation as the "anti-Turkish pope" for saying that Turkey's European Union membership would be a "a grave error against the tide of history" when he was still Cardinal Joseph Ratzinger.

Copyright AFP (Agence France-Presse), 2006