Bernie Sanders greeted briefly by Pope Francis before leaving Vatican

VATICAN CITY, April 16 (UPI) -- Democratic presidential candidate Sen. Bernie Sanders met briefly with Pope Francis early Saturday, with the candidate saying it was "the highlight of the trip" to the Vatican.

Sanders had been invited to a papal conference on social justice, asked to speak on his presidential campaign's core message, about returning America to a "moral economy."

Sanders delivered a 15-minute address to the conference Friday, which Francis did not attend while he prepared for a trip to Greece to meet with Syrian refugees.

Sanders and his family stayed at a hotel near the Vatican on Friday night, then received a message from the conference's host, Bishop Marcelo Sanchez Sorondo, that the pope wished to greet Sanders and his wife, Jane.

The meeting lasted about five minutes.

The meeting happened at the papal residence in the foyer of the Domus of Santa Marta during the pope's usual breakfast time, around 6 a.m. It was not announced to the press beforehand and no photos were taken.

The Vatican is loathe to wade into electoral politics and was careful, even after the meeting, to avoid the appearance the pontiff had endorsed a candidate in the U.S. presidential race.

Francis, speaking to the media during his trip to the Greek island Lesbos, said the meeting was a courtesy to thanks Sanders for his visit.

"When I came down, I greeted them, shook their hands and nothing more. This is good manners. It's called good manners and not getting mixed up in politics," the pope said. "If anyone thinks that greeting someone means getting involved in politics, they should see a psychiatrist."