ROME — Italian paramilitary police blocked a boulevard Sunday to prevent a march by victims of sexual abuse by Roman Catholic clerics from reaching St. Peter’s Square at the Vatican.

When the Vatican spokesman, the Rev. Federico Lombardi, came to speak with organizers Sunday evening, a protester shouted “Shame, shame” in Italian. Father Lombardi later said by telephone that he had come to greet the organizers but when he saw “it wasn’t going to be easy” he left, escorted by the police.

He said that if organizers wanted to see him he would “gladly” receive them inside his office. Shortly after that, one of the organizers, Gary Bergeron, did meet briefly with him, and the two agreed to have another meeting later.

The Vatican routinely prohibits activities it does not sponsor from using St. Peter’s Square.

The event, which aimed to show victims worldwide that they are not alone, was organized by Mr. Bergeron and Bernie McDaid, who are both from Boston and who as children were both abused by the same priest several years apart. Mr. Bergeron said he told Father Lombardi that the abuse survivors have been “waiting a lifetime to be able to stand up and speak out.”