Democratic presidential hopeful Bernie Sanders 's plan to attend a Vatican-sponsored conference later this month has sparked some diplomatic controversy, with a senior Vatican official accusing him of showing "monumental discourtesy" in seeking an invitation.

Sanders earlier on Friday had said the Vatican had invited him to attend a conference on social and economic issues to be held on April 15, just days before the New York primary. The Pontifical Academy of Social Sciences is hosting the event.

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"It was an invitation from the Vatican," Sanders said on MSNBC's "Morning Joe." "I was very moved by the invitation."

But the senior Vatican official, Margaret Archer, president of the Pontifical Academy of Social Sciences, said it was Sanders who made "the first move" to attend the event.

She told Bloomberg on Friday that Sanders had done so "for the obvious reasons," a comment that suggested a political motivation.

“I think in a sense 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 added. However, Bishop Marcelo Sánchez Sorondo, chancellor of academy, formally invited Sanders to attend the meeting in a letter dated March 30 and provided to The Hill by Sanders' campaign.