Pope Leo XIV set the tone for his papacy on Sunday with a call to stop exploiting nature and marginalising the poor at a mass attended by world dignitaries including Ukrainian President Volodymyr Zelensky and US Vice President JD Vance.

Ten days after Chicago-born Robert Francis Prevost became the first US head of the world’s 1.4 billion Catholics, an estimated 200,000 people gathered to see his inaugural mass in St Peter’s Square.

The 69-year-old made his debut tour in a popemobile, smiling, waving energetically and blessing the cheering crowds at the Vatican.

In front of leaders including Zelensky and Vance, he then gave a homily where he called for the Church to be a transformational force in a world of division and hatred.

“In this our time, we still see too much discord, too many wounds caused by hatred, violence, prejudice, the fear of difference, and an economic paradigm that exploits the Earth’s resources and marginalises the poorest,” he said.

Prevost, who was made a cardinal only in 2023 and is unknown to many Catholics, has repeatedly emphasised the importance of peace and social justice in his first few days as pope.

Later on Sunday, he was due to hold his first private audience with Zelensky.

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“The martyred Ukraine is waiting for negotiations for a just and lasting peace to finally happen,” Leo said during a prayer at the end of the ceremony.

Yona Tukuser, a 39-year-old artist from Odessa in Ukraine who was amongst the crowd in St Peter’s Square, said Leo was “a pope for peace” who would “work very hard to build a bridge for dialogue”.

– First US pope –

Leo has made history as the first pontiff from the United States, and his home country was represented on Sunday by Vance, who converted to Catholicism in 2019, and US Secretary of State Marco Rubio, also a Catholic.

Vance — the last world leader to meet with the late Pope Francis the day before he died last month — queued up to shake Leo’s hand along with the other dignitaries.

He did not have a private audience scheduled for Sunday but this could still happen as he is not due to return to Washington until Monday.

Maria Grazia La Barbera, 56, a pilgrim from Palermo in Sicily, said Leo was “the right person at the right time” to lead the Church.

“He will certainly do what he promised: knocking down walls and building bridges,” she said.

Before becoming pope, Leo reposted on his personal X account criticism of US President Donald Trump’s administration over its approach to migration and also pilloried Vance.

READ ALSO: ‘I’m Deeply Pained,’ Pope Leo XIV Emotionally Begs World Leaders To End Wars In Ukraine, Gaza

On Sunday, the pope — who spent many years as a missionary in Peru — warned against “closing ourselves off in our small groups”.

“We are called to offer God’s love to everyone, in order to achieve that unity which does not cancel out differences but values the personal history of each person and the social and religious culture of every people,” he said.

Leo’s elevation has sparked huge enthusiasm in the United States, but also some consternation elsewhere that a country with an already outsize political and military role in the world now boasts one its foremost spiritual leaders.

“There is going to be extra weight because he is American, I think there’s going to be a lot of extra eyes, and maybe criticisms,” said Sophia Tripp, a 20-year-old student visiting from Leo’s hometown of Chicago.

But she said she hoped he would “bring people together”, adding: “We are all human, and we should just all be loving to one another.”

Other guests on Sunday included German Chancellor Friedrich Merz, Italian Prime Minister Giorgia Meloni and European Commission President Ursula von der Leyen.

President Dina Boluarte of Peru — where the pope holds citizenship — Canadian Prime Minister Mark Carney, Israeli President Isaac Herzog and Colombia’s President Gustavo Petro also attended, as did a host of faith leaders and European royals.

READ ALSO: Pope Leo XIV Outlines A Path For A Modern Church That Follows Francis’ Steps

Italian authorities deployed thousands of security officers for the event, alongside snipers on rooftops and anti-drone operations.

– ‘Fear and trembling’ –

Leo XIV was elected as the 267th pope on May 8 after a conclave vote of cardinals that lasted less than 24 hours.

Succeeding the charismatic but impulsive Francis, he took over a Church still battling the fallout of the clerical child abuse scandal, and trying to adapt to the modern world.

Leo acknowledged on Sunday some trepidation in his new role.

“I was chosen, without any merit of my own, and now, with fear and trembling, I come to you as a brother who desires to be the servant of your faith and your joy,” he said.

Ahead of the mass, Leo visited the tomb of Saint Peter — who in the Christian tradition was one of the Twelve Apostles of Jesus Christ, and the first pope — in the basilica that bears his name.

He then received the pontifical emblems — the pallium, a strip of cloth worn around the neck, and the fisherman’s ring, which is forged anew for each pope and which he will wear on his finger until he dies, when it will be destroyed.