The Vatican treated new recruits of its police force and Swiss Guard to beer and popcorn at a special screening of the new film The Greatest Beer Run Ever on Monday, topped off by a meeting with one of its stars - Russell Crowe.

Crowe, in Italy for the Rome Film Festival, dropped into the Vatican's small projection room - which seats only about 50 people - to greet the audience between two back-to-back screenings.

The film is set in New York City and Vietnam in 1967 and is based on the true story of John "Chickie" Donahue, who brought cans of beer from the neighbourhood watering hole to Vietnam to lift the spirit of friends fighting there.

Donahue is played by Zac Efron and Crowe plays hardened and hard-drinking war photographer Arthur Coates. Bill Murray plays a crotchety and super-patriotic World War Two veteran who runs the bar in Manhattan's Inwood neighbourhood.

The Vatican event was organised by Fr Andrew Small, an official at the Vatican's Commission for the Protection of Minors, who has a cameo appearance playing a neighbourhood parish priest.

"I just feel a kinship with the men here in the Vatican who are protecting us and I thought that inviting them and friends to a movie is what you do when you want to be friendly," Small said.

Reuters spoke to some recruits who enjoyed the film, a comedy-drama whose backdrop is how the war deeply divided American families, drinking buddies and society at large.

In the film Donahue also carried a rosary from a neighbourhood mother to give to her son in Vietnam but he was killed before Donahue could find him.

While the film was being projected on Monday, Small went to Pope Francis' nearby residence and the pope blessed several dozen rosaries that were given to those at the screening.

Crowe later toured St Peter's Basilica and was given a rare, close-up look at Michelangelo's Pieta, allowed to go behind the bulletproof glass that seals off a side chapel where it is on display.