Archbishop Charles Chaput told a North Dakota audience Thursday that Pope Francis had assured him he will visit Philadelphia for three days next year, and the Vatican seemed to confirm it, but the Archdiocese of Philadelphia insisted Friday that Chaput's remarks were off-the-cuff and unofficial.

"There has been no official confirmation by the Vatican or The Holy See of Pope Francis' attendance at the 2015 World Meeting of Families in Philadelphia," communications director Kennet Gavin said in a statement Friday Morning.

However, Vatican spokesman Rev. Federico Lombardi on Friday said Francis had expressed "his willingness to participate" in the triennial World Meeting, which is scheduled for September 22-27 of next year.

The international gathering is expected to draw about 300,000 visitors a day for its conferences promoting traditional family values and Catholic teachings. But but a visit by the pope to say Mass — traditionally scheduled for the final day — would likely draw more than a million.

"The pope will be with us the Friday, Saturday and Sunday of that week," the Catholic News Service reported Chaput as saying during the opening Mass of the Tekakwitha Conference in Fargo. He also invited those in attendance to come to Philadelphia for gathering.

Nevertheless, the archdiocese said Friday it expected that "any official confirmation will come approximately six months prior to the event."

But Lombardi said Francis is already "considering invitations" from New York, Washington, the United Nations, which will be in session at that time, and Mexico.

A three-day visit would be departure from tradition, since Francis' predecessors — Pope Benedict XVI and John Paul II — usually appeared to say Mass on the final day of these popular international gatherings.

In March, Chaput led a delegation of city and state civic leaders, including Mayor Nutter and Governor Corbett, to meet with Francis in Rome and formally invite him to the city for the World Meeting.

Those officials had only brief conversations with Francis during his regularly scheduled public audience in St. Peter's Square, but came away voicing confidence that Francis would come.

Officials of the Pontifical Council for the Family, the Vatican office that sponsors the World Meetings, also hinted strongly in March that Francis was strongly inclined to attend, saying that only ill health would likely deter a visit.

Nevertheless, Chaput's remarks appeared to take the archdiocese by surprise. It was not until late in the morning that it issued a response.

"We still expect that any official confirmation will come approximately six months prior to the event," it said.

"Archbishop Chaput has frequently shared his confidence in Pope Francis' attendance at the World Meeting and his personal conversations with the Holy Father are the foundation for that confidence.

"We are further heartened and excited by the comments of the Vatican Press Office regarding Pope Francis' 'willingness to participate in the World Meeting of Families.' While Archbishop Chaput's comments do not serve as official confirmation, they do serve to bolster our sincere hope that Philadelphia will welcome Pope Francis next September. "

The visit would be Francis' first to the United States since he became pope in March 2013.

The last papal visit to Philadelphia was Pope John Paul II's 1979 trip to the city.

Emily Babay of contributed to this article.