U.S. Democratic presidential candidate Bernie Sanders will speak at an event in the Vatican next week, likely broadening his appeal to Catholic voters ahead of crucial nominating contests in a series of northeastern states.

Like Pope Francis, Sanders has made economic inequality and the plight of the working class a central tenet of his message. Sanders' April 15 visit to Vatican City, where he will give an economic address at a conference, will come just days before Democrats in New York vote in their state primary.

The trip may help the Vermont senator amplify the anti-corporate line of attack he has employed against Democratic rival Hillary Clinton as he tries to keep his insurgent campaign for the Nov. 8 presidential election alive.

Sanders a 'big, big fan' of pope

Sanders, who would be the first Jewish U.S. president if elected, described himself on MSNBC as a "big, big fan of the pope," who leads the world's 1.2 billion Catholics.

Speaking to reporters in New York later, Sanders said he hoped to meet with Francis.

"The pope's schedule is determined by the Vatican but I would certainly be enthusiastic about that," said Sanders, 74, the Brooklyn-born son of Polish-Jewish immigrants.

Democratic presidential frontrunner Hillary Clinton campaigns Thursday in New York City. Clinton has scored victories over Sanders in Florida, Louisiana, Massachusetts, and Texas, all of which are more than one-quarter Catholic. (Andrew Renneisen/Getty Images)

A meeting with the Argentine pontiff could provide an electoral boost to Sanders, who has trailed former secretary of state Clinton in support among America's Catholic Democrats.

"Pope Francis has criticized the 'make money at all cost' capitalist mentality and called for more compassion for the poor," said Brad Bannon, a Democratic strategist in Washington. "That's exactly the way Bernie Sanders wants to define his campaign against Clinton."

Clinton has scored victories over Sanders in Florida, Louisiana, Massachusetts, and Texas, all of which are more than one-quarter Catholic.

Catholic voters up for grabs

A survey by the Pew Research Center earlier this year found that while almost 70 per cent of Catholic Democrats thought Clinton would make a good president, just 46 per cent thought Sanders would be one.

"This is a great play for Sanders because it ties directly to his messaging related to income equality, it puts him on the world stage as a leader, and it does it with an institution and leader important to a key voting bloc in a state where every vote is going to count heading into the primary," said Virginia-based Democratic strategist Bud Jackson.

Roughly one in five U.S. adults say their primary religious affiliation is with the Catholic Church, according to the Pew Research Center. (Alberto Pizzoli/AFP/Getty Images)

Sanders was invited to speak at the Vatican event by the Vatican, a senior papal official said, denying a report that Sanders had invited himself.

"I deny that. It was not that way," Monsignor Marcelo Sanchez Sorondo told Reuters. Sorondo, a close aide to Pope Francis, is chancellor of the Pontifical Academy of Social Sciences, which is hosting the event.

Late April brings nominating contests in Connecticut, Maryland, Pennsylvania, and Rhode Island, all states with large populations of Catholic voters.