The pope's office has distanced Francis from a rare invitation to US presidential candidate Bernie Sanders to attend a conference at the Vatican this week.

The pope's spokesman, Father Federico Lombardi, told local media that the Vermont senator had been invited "not by the pope but by the Pontifical Academy of Social Sciences."

"For the moment there is no expectation that there will also be a meeting with the pope," Lombardi told the Italian news agency Ansa.

Meanwhile, officials at the Vatican-based academy can't agree whether it was a good idea to invite Bernie Sanders to attend the conference, which will focus on social justice and the environment, amid fears the attendance will cast a political slant on the event.

Sanders, who would be the first Jewish US president if elected, is the only 2016 political candidate to have accepted an invitation to attend the event on April 15-16. A meeting with the Argentine pontiff could provide an electoral boost to Sanders, just days before the New York primary on April 19. But the remarks from the Pontifical Academy appear to have diminished that possibility.

Over the weekend, Academy President Margaret Archer accused Sanders of vying for a spot at the event without properly informing her office. Archer said that the academy had not invited Sanders, but that he had pushed his way to a invitation — something the campaign has vigorously denied.

"Sanders made the first move, for the obvious reasons," Archer told Bloomberg. "He may be going for the Catholic vote but this is not the Catholic vote and he should remember that and act accordingly — not that he will."

Archer took issue with Sanders' failure to contact her before publicizing that he will attend the event, characterizing it as a "monumental discourtesy."

But Bishop Marcelo Sanchez Sorondo, the chancellor of the Academy who is senior to Archer and is also a close aide to Pope Francis, denied Archer's version of events. Sorondo told Reuters that he had issued the invitation, and denied that the senator had invited himself.

"This is not true and she knows it. I invited him with her consensus," Sorondo said.

A copy of the invitation given to reporters claimed it was extended "on behalf" of Archer and conference organizers. The document was signed by Sorondo.

The Sanders campaign said the senator had received the invitation "from the Vatican" and characterized Archer's comments as "categorically untrue."

The trip has also caused a small stir among pundits ahead of the April 19 New York primary, as Sanders will be forced to take a break from campaigning for a few days to fly to Rome and back. The campaign will board a charter immediately after a highly-anticipated Democratic debate in New York that Sanders had been pressuring Clinton to accept on April 14.

Sanders Campaign manager Jeff Weaver told Bloomberg TV that although the trip to the Vatican comes just a few days before a must-win primary in New York, the invitation represents a "can't miss opportunity," arguing that "some things are more important than politics."

Sanders has made economic inequality and the plight of the working class a central tenet of his message and has often quoted Pope Francis on those issues in campaign speeches. The trip may help the US senator amplify that message as he tries to keep his insurgent campaign for the Democratic nomination alive.

In announcing on Friday that he had accepted the invitation to go to Vatican City this weekend, Sanders said he was a "big, big fan of the pope."

"Obviously there are areas that we disagree on — women's rights and gay rights, but he has played an unbelievable role of injecting a moral consequence into the economy," Sanders said on MSNBC's__Morning Joe_._

"People think Bernie Sanders is radical, [but] read what the pope is writing," he added.

But Sanders has struggled with Catholic voters nationally in the Democratic primary race. A survey by the Pew Research Center earlier this year found that while almost 70 percent of Catholic Democrats thought Clinton would make a good president, while just 46 percent thought Sanders would be one.

Over the weekend, Weaver denied that the senator was using the Vatican trip as a way to broaden his appeal to Catholic voters ahead of crucial nominating contests in a series of Northeastern states.