Pope Leo XIV has called for a ceasefire in Gaza and the release of all hostages, as well as "no more war", as he led a prayer to the Virgin Mary from the balcony of St Peter's Basilica.
He also called for an "authentic and lasting peace" in Ukraine, and welcomed the ceasefire between Pakistan and India which was announced yesterday.
The noon (11am Irish time) prayer drew thousands of people anxious for a closer look at the modest pontiff, born Robert Francis Prevost, who before becoming the first pope from the United States spent much of his life as a missionary in Peru.
Pope Leo championed religious life in his public address, saying the church has a "great need" for its priests and nuns, while young people require "credible models".
"Today brothers and sisters, I therefore have the joy of praying with you and all the people of God for vocations, especially those to the priesthood and consecrated life. The church has such a great need for them!" said the American pope, who was elected on Thursday, adding that young people needed to be able to "look up to credible models of generous dedication to God".
Cardinals chose Leo as the 267th pope at a secret conclave on Thursday, praying he could heal rifts within the Church, renew faith among the world's 1.4 billion Catholics and address a host of modern-day challenges weighing on the more than 2,000-year-old institution.
Addressing cardinals yesterday, the 69-year-old Pope Leo called himself a "humble servant of God... and nothing more than this", and an "unworthy successor" to St Peter, according to a transcript released by the Vatican.
A steady stream of pilgrims and worshippers began to gather in St Peter's Square this morning, bearing flags and Catholic symbols from across the globe. Priests and nuns mingled with the crowds, with many groups of young people, some playing guitars and singing songs.
Resfina Macoy Torrevillas, a 68-year-old from San Diego, California, said Pope Leo's appearance would be the "highlight" of her group's pilgrimage.
"We're hoping for a good year, because the Catholic Church is challenged right now, especially in the USA."
She hoped the new pope could help mend that: "God moves in mysterious ways."
Tribute to Francis
In the first clues as to the direction of his pontificate, Pope Leo said yesterday he would be driven by the legacy of his predecessor, Pope Francis - who died on 21 April aged 88 - "with his example of complete dedication to service and to sober simplicity of life".
Leo made an unannounced visit to pray before Francis's simple marble tomb inside Santa Maria Maggiore basilica early yesterday evening. The church was a favourite of Francis and worshippers have continued to line up to pay their respects there.
Cardinals describe Leo as in the mould of Francis, with a commitment to the poor and disadvantaged, and a focus on Catholics in far-flung areas away from Rome.
As an Augustinian and former missionary, he also believes the Church should be committed to "the missionary conversion of the entire Christian community", as he told cardinals.
Before visiting Francis's tomb, Leo visited an Augustinian shrine southeast of Rome, the Basilica Sanctuary of the Mother of Good Counsel - underscoring the importance to the new pontiff of the religious order, which is focused on community and collaboration.
The new pope's personal style is seen to be less direct than the sometimes impulsive Francis, a progressive who shook up the Church and often ruffled feathers within the Roman Curia, or government of the Holy See, during his 12-year papacy.
Cardinal Pierbattista Pizzaballa, the Latin Patriarch of Jerusalem, described Leo as "a person who immediately inspires a lot of confidence, a mild man who knows how to listen..."
"We are at the beginning of his pontificate, but already the first steps give us great courage and comfort. Even the reaction of the people, so beautiful and enthusiastic, says a lot," Cardinal Pizzaballa told the Corriere della Sera daily on Sunday.
Now for journalists, diplomats
Pope Leo's Regina Caeli prayer to the Virgin Mary, recited at Easter and its aftermath, kicks off a busy week of meetings and audiences.
Tomorrow, he will be officially presented to the international media who came to Rome to cover his election.
He plans to meet diplomats to the Vatican on Friday and then on Sunday 18 May will preside over the inaugural mass at St Peter's to mark the beginning of his pontificate.
The following week is marked by Leo's first general audience on 21 May - a normally weekly event by the pope which includes readings from Scripture and a homily for the public.
He also plans to meet with members of the Roman Curia and Vatican officials on 24 May.
In one of his first decisions, Leo has already said the heads of dicasteries, or Vatican departments, will keep their positions for now. Those roles had been suspended between Francis's death and the new pope's election.
"The Holy Father wishes to reserve some time for reflection, prayer and dialogue, before any definitive appointment or confirmation," the Vatican said.
Meanwhile, the pontiff begins his tours to take possession of Rome's four papal basilicas - including a scheduled visit to Santa Maria Maggiore on 25 May.
Francis named Leo a cardinal in 2023 after choosing him to lead the powerful Dicastery of Bishops, which advises the pontiff on bishop appointments.
However he has been largely unknown outside the Vatican.
He spent approximately two decades in Peru on missions, taking Peruvian citizenship and learning Spanish - which he used during his first address on Thursday from St Peter's Basilica.
