The smallest army and one the world's oldest standing armies has welcomed 34 new recruits from Switzerland to serve the Roman Catholic pope.

In their oath-taking the new Swiss Guards were sworn in on May 6 in an elaborate ceremony in Vatican City in which the guards promised to protect the Pope, even "sacrificing if necessary also my own life," Catholic News Agency reported.

Pope Francis addressed the new recruits and expressed his appreciation that young people "choose to dedicate some years of their lives in generous service to the Successor of Peter and to the ecclesial community."

The Swiss Guard was founded in 1506 by Pope Julius II, deposed twice and re-established in 1800. It remains tasked with protecting the pope and his residence.

Francis said, "With you I thank the Lord, the source of all good, for the various gifts and vocations.

"He has entrusted to you, and I pray that those who are now beginning their service may respond fully to Christ's call, following Him with faithful generosity."

The Chaplain to the Swiss Guard, Father Thomas Widmer offered the Guards a reflection on the spiritual meaning of "oath-taking," Vatican News reported.

He said their sharp, military bearing is at its most impressive and beautiful when it is combined with interior courage in defending the Gospel.

"You, as Christian soldiers, remember that you increase in courage and infinite power because Almighty God is with you," Widmer said.

"Your oath, dear Guards, in essence says: I am capable of remaining faithful and steadfast in representing and living out universal values and thus bearing fruit also for the good of society."

Entry requirements include being Swiss, Catholic, at least 1.74 meters (5 feet 7 inches) tall, under 30 years old, and male.

The swearing-in ceremony of the smallest army in the world always takes place on May 6 - in memory of the 1527 Sack of Rome, an uprising at the time.

This year Switzerland's President Guy Parmelin met the Pope in the Vatican for the swearing-in.

The Pontifical Swiss Guard has increased from 110 to 135 men since 2018.