Vatican City: Pope Leo XIV celebrated his first Mass on Friday in the Sistine Chapel where he was elected less than 24 hours earlier, warning of the dangers caused by a lack of faith and hoping the Catholic Church could be a beacon lighting the world's "dark nights".

Leo, the former Cardinal Robert Prevost and the first US Pope, looked calm as he delivered the Mass in the famous, frescoed chapel with the same cardinals who chose him to be the 267th pontiff and the successor to Pope Francis.

Dressed in relatively simple white and gold vestments, Pope Leo, who was born in Chicago but spent two decades as a missionary in Peru, said a few words in English before continuing his homily in fluent Italian.

In the homily, Pope Leo, 69, painted a picture of the Church he would like to see, saying he would seek to serve as the "faithful administrator" for the Church as a whole.

The new Pope, who leads 1.4 billion Catholics around the world, acknowledged that the Christian faith is sometimes "considered absurd" and the preserve of "the weak and unintelligent".

"A lack of faith is often tragically accompanied by the loss of meaning in life, the neglect of mercy, appalling violations of human dignity, the crisis of the family and so many other wounds that afflict our society," he said.

May 18 inauguration
An inauguration Mass for Pope Leo will be held in St Peter's Square on May 18, the Vatican said.

World and religious leaders are invited to the inauguration, which marks the formal launch of a papacy. Pope Francis' inauguration in 2013 attracted a crowd estimated at 2,00,000 people.

The Vatican also said the new Pope will leave senior Vatican officials in their roles for the time being, giving him time to decide before making definitive appointments.

All Vatican senior officials, appointed for five-year terms, serve at the pleasure of the Pope. A new pontiff usually rolls over existing mandates at least initially before deciding whether to change key positions.

The pope was elected at the end of a two-day conclave that was wrapped up on Thursday evening when white smoke billowed from the chimney on the Sistine Chapel.

Given the nature of the conclaves, when cardinals are shut away from the world and sworn to secrecy, little or nothing is likely to emerge, at least for now, about how Pope Leo obtained the required two-thirds majority of the vote so swiftly.

The successor to Pope Francis, who died last month at the age of 88, inherits a number of major challenges, ranging from a budget shortfall to divisions over whether the Church should be more welcoming towards the LGBT community and divorcees, and should let women play a greater role in its affairs.

He will also have a packed agenda, with the Vatican celebrating a Holy Year that brings millions of additional tourists to Rome.

The first US Pope
Before his election as the Pope, US cardinals had largely been written off as papal contenders because of a widespread assumption that a superpower Pope could not run the global Church. 

However, he also holds Peruvian citizenship, meaning that he has deep knowledge of both the West and less developed nations.

US President Donald Trump was quick to congratulate Pope Leo. However, the new pope has a history of criticising Trump and Vice President JD Vance's policies, according to posts on the X account of Robert Prevost.

Pope Leo worked for decades in the north of Peru, first as a missionary and later as Bishop of Chiclayo from 2015 to 2023. Catholics took to the streets of the small city in northwestern Peru, and church bells rang out to celebrate the election of a man who they embrace as one of their own.

One of the clues to what kind of a Church leader Pope Leo will be was in his choice of name. The last pope with this name was Leo XIII, who led the Church from 1878-1903. He was known for his devoted focus on social justice issues.

Prevost became a cardinal only in 2023. He has given few media interviews and is known to have a shy personality.

Francis brought him to Rome two years ago to head the Vatican office in charge of choosing which priests should serve as Catholic bishops, meaning he has had a hand in selecting many of the world's bishops.