Why couldn't the Rabbi's funeral be in the Old city?

I read the following: In accordance with a halakhic ruling by Rabbi Chizkiyahu Nebenzahl, Rav of the Old City, his casket was not allowed to be brought into the Old City for eulogies at his yeshiva, Aish HaTorah. Rather, the funeral began at a synagogue near his home in Kiryat Sanz, and proceeded to interment on Har HaMenuchot.