Pope Francis wants to open his arms to the world's most vulnerable people

Pope Francis has vowed to embrace the world's "weakest and poorest" and called on world leaders to shun "destruction" at his inaugural mass in St Peter's Square.

Francis was interrupted by applause several times during his homily, including when he spoke of the need to serve one another with love and tenderness and not allow " hatred, envy and pride to defile our lives".

The Pope must "open his arms to protect all of God's people and embrace with tender affection the whole of humanity, especially the poorest, the weakest, the least important," Francis, the first Jesuit pope, said.

"He must be inspired by lowly, concrete and faithful service," said Francis, who as a Jesuit has taken a vow of poverty.

"I would like to ask all those who have positions of responsibility in economic, political and social life ... Let us not allow omens of destruction and death to accompany the advance of this world.

"It means respecting each of God's creatures and respecting the environment in which we live.

"It means protecting people, showing loving concern for each and every person, especially children, the elderly, those in need, who are often the last we think about."

The Fisherman's Ring

The new pontiff officially began his ministry as the 266th pope and leader of the world's 1.2bn Roman Catholics when he earlier received the ring and pallium symbolising his new papal powers at the Vatican.

The pallium is a strip of lambswool that represents the Pope's role as a shepherd and the Fisherman's Ring is named in honour of the first pope St Peter, a fisherman by trade.

The grand ceremony started at 8.30am GMT in a sun-drenched St Peter's Square before about 200,000 people, including royalty, political and religious leaders.

The biggest delegation came from Argentina, led by President Cristina Kirchner, who held a private meeting with Pope Francis on Monday.

Britain was represented by the Duke of Gloucester, Kenneth Clarke MP and Baroness Warsi. The Queen and Prime Minister David Cameron did not attend.

Controversial Zimbabwean President Robert Mugabe also made the journey to Rome in defiance of an EU travel ban, which does allow him to attend events within the Vatican state boundary.

Before the proceedings began, Francis toured a crammed St Peter's Square, kissing babies and blessing a disabled man.

In another sign of the informality that is already a mark of his papacy, Francis abandoned the bullet-proof popemobile frequently used by his more formal predecessor Benedict, to tour the square.

Francis wore a plain white papal cassock and black shoes in contrast to the luxurious red loafers that attracted attention under Benedict.

"Go Francis! We Will Be With You Wherever You Go!" read a sign held up by a group of Brazilian nuns in St Peter's Square.

Sister Rosa, an elderly Italian nun, said she expected the pope would be "another St Francis on Earth for love, goodness, poverty and humility".

Crowds had been pouring into the square and surrounding streets since before dawn.

The former archbishop of Buenos Aires, Jorge Mario Bergoglio was the surprise choice at a conclave of cardinals to find a successor to 85-year-old Benedict, who last month brought a sudden end to a papacy, saying he was too old to carry on.

After the Mass, Pope Francis met many of the world leaders, including Mr Mugabe, before having lunch.

Leaders of the Eastern Catholic Rite were also at the ceremony, including Bartholomew I, the Ecumenical Patriarch of Constantinople.

Bartholomew I became the first patriarch from the Istanbul-based church to attend a papal investiture since the two branches of Christianity split nearly 1,000 years ago.

Also attending for the first time was the chief rabbi of Rome.

Their presence underscores the hopes for ecumenical and interfaith dialogue in this new papacy given Francis' own work for improved relations and his namesake St Francis of Assisi.

In a gesture to Christians in the East, the pope prayed with Eastern rite Catholic patriarchs and archbishops before the tomb of St Peter and the Gospel was chanted in Greek rather than the traditional Latin.

On Wednesday and Thursday, Francis will hold meetings at the Vatican before he holds a face-to-face meeting with Benedict at Castel Gandolfo, just outside Rome, on Saturday.